{"id":5146,"date":"2025-09-05T22:08:02","date_gmt":"2025-09-06T03:08:02","guid":{"rendered":"https:\/\/sites.owu.edu\/geog-291\/?p=5146"},"modified":"2025-09-05T22:08:02","modified_gmt":"2025-09-06T03:08:02","slug":"becker-week-3","status":"publish","type":"post","link":"https:\/\/sites.owu.edu\/geog-291\/2025\/09\/05\/becker-week-3\/","title":{"rendered":"Becker- Week 3"},"content":{"rendered":"<p><span style=\"font-weight: 400\">Mitchell- Chapter 4<\/span><\/p>\n<p><b>Why Mapping Density?<\/b><\/p>\n<ul>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Shows concentrations of features<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Good for overall patterns<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Density map uses uniform areal unit to show feature distributions<\/span><\/li>\n<\/ul>\n<p><b>Deciding What to Map<\/b><\/p>\n<ul>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Map density in one of two ways:<\/span>\n<ul>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Shading defined areas based on density values<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Create a density surface<\/span><\/li>\n<\/ul>\n<\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Mapping the density of points or lines is usually done using density surface<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Can map data already summarized by defined areas (ex: census tracts, forest districts, administrative boundaries)<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Can map density of features or of feature values<\/span><\/li>\n<\/ul>\n<p><b>Two Ways of Mapping Density<\/b><\/p>\n<ul>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Density map gives you density per area measurement<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">By Defined Area:<\/span>\n<ul>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Dot density maps show density graphically, rather than showing density value<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">To calculate density value for each area, divide total number of features by area of polygon<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Each area then shaded based on calculated value<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Can see areas of higher density but not centers of density<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Could also create shaded fill map<\/span><\/li>\n<\/ul>\n<\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">By Density Surface:<\/span>\n<ul>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Density surface usually created in GIS as a raster layer<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Each cell gets density value based on number of features within radius of cell<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">This provides more detailed info, but more effort<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Point data used to create density surface may be<\/span>\n<ul>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Locations of features<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Sample points you\u2019ve collected data for<\/span><\/li>\n<\/ul>\n<\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Can create density surfaces for individual locations or linear features<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Can also create contour map<\/span><\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<p><b>Mapping Density For Defined Areas<\/b><\/p>\n<ul>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Dot density map or calculated density for an area<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Calculating Density Value for Defined Areas:<\/span>\n<ul>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">To do so, add new value for feature, then assign density value by dividing value being mapped by area of designated polygon<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Make sure units align<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Use range of shades of a couple hues<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Density treated as ratio and graphed like one<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">ArcGIS lets you calculate density easily, but values are temporary and not stored in database<\/span><\/li>\n<\/ul>\n<\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Creating a Dot Density Map:<\/span>\n<ul>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Map each area based on total count\/amount and specify how much each dot represents<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">GIS divides value of polygon by amount represented by a dot to find how many dots to draw in an area<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Give quick sense of density in a space<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Dots represent totals rather than calculated density values<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Specify dot value and size (don\u2019t be scared to play around)<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Display dots based on smaller areas, draw boundaries of larger areas<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">That way boundaries won\u2019t obscure dots<\/span><\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<p><b>Creating a Density Surface<\/b><\/p>\n<ul>\n<li style=\"list-style-type: none\">\n<ul>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Created in GIS raster layers (good for showing where point or line features are concentrated)<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">To create density surface GIS:<\/span>\n<ul>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Defines a neighborhood (based on specified search radius) around each cell center<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Totals number of features in this neighborhood<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Divide number by area of neighborhood<\/span><\/li>\n<\/ul>\n<\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">If using data value instead of features GIS:<\/span>\n<ul>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Totals that value for all features in neighborhood<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Divides that by area of neighborhood<\/span><\/li>\n<\/ul>\n<\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Parameters that affect how GIS calculates density<\/span>\n<ul>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Cell size<\/span>\n<ul>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Determines how coarse or fine patterns will appear (smaller cell size = smoother surface, but longer processing time and more storage space)<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Larger cell = faster processing but coarser surface<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">In general, set cell size to have 10-100 cells per density unit<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">To calculate cell size<\/span>\n<ul>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Convert density units to cell units<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Divide by number of cells per density unit<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Take square root of cell area to get length of one side<\/span><\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Search Radius<\/span>\n<ul>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Larger the search radius the more generalized the patterns in the density surface will be (GIS also considers more features when calculating value of each cell)<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Smaller radius shows more local variation (be careful not to make too small or you\u2019ll lose broader patterns)<\/span><\/li>\n<\/ul>\n<\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Calculation Method<\/span>\n<ul>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Two Methods For Calculating Cell Values:<\/span>\n<ul>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Count features in search radius of each cell<\/span>\n<ul>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Result is a series of overlapping rings<\/span><\/li>\n<\/ul>\n<\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Weighted method<\/span>\n<ul>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Uses mathematical function to give more weight to values closer to center of cell<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Weighting drops off rapidly for features outside search radius<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Every cell in layer is counted and assigned a value<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Smoother, more generalized surface and easy-to-interpret patterns<\/span><\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Units<\/span>\n<ul>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Choose a value for units that reflects features being mapped<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">If areal units are different than cell units, legend values are extrapolated<\/span><\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">If you have data summarized by defined areas create a density surface:<\/span>\n<ul>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Use center points (centroids) of defined areas to create density surface based on value assigned to each area<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Do this to highlight patterns in the map with less emphasis on individual polygons<\/span><\/li>\n<\/ul>\n<\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Display density surface using either graduated colors or contours<\/span>\n<ul>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Graduated colors<\/span>\n<ul>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Classify unique density values for each cell to see patterns<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Create custom class ranges or specify standard classification scheme and let GIS create classes for you<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Classification schemes:<\/span>\n<ul>\n<li style=\"font-weight: 400\"><b>Natural breaks<\/b><span style=\"font-weight: 400\">&#8211; based on groupings of data values<\/span><\/li>\n<li style=\"font-weight: 400\"><b>Quantile<\/b><span style=\"font-weight: 400\">&#8211; each class same number of cells inside<\/span><\/li>\n<li style=\"font-weight: 400\"><b>Equal interval<\/b><span style=\"font-weight: 400\">&#8211; difference between high and low value the same for each class<\/span><\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<ul>\n<li><b>Standard Deviation<\/b><span style=\"font-weight: 400\">&#8211; classes defined by number of standard deviations from mean of all values in layer<\/span><\/li>\n<\/ul>\n<ul>\n<li style=\"list-style-type: none\">\n<ul>\n<li style=\"list-style-type: none\">\n<ul>\n<li style=\"list-style-type: none\">\n<ul>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">GIS lets you specify number of classes to assign the density values<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Using a few classes highlights the areas with highest density but may not show subtleties in the patterns<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Density surfaces usually displayed using different shades of a single color<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">If using standard deviation use shades of one color for values above mean, and shades of a different color for values below the mean<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Areas of higher value use darker colors<\/span><\/li>\n<\/ul>\n<\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Using Contours<\/span><\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<ul>\n<li><b>Contour lines<\/b><span style=\"font-weight: 400\"> connect points of equal density value on the surface<\/span><\/li>\n<\/ul>\n<ul>\n<li style=\"list-style-type: none\">\n<ul>\n<li style=\"list-style-type: none\">\n<ul>\n<li style=\"list-style-type: none\">\n<ul>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Most GIS software makes contour lines automatically (just specify contour interval)<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Contours are good for showing rate of change across the surface (closer contours = more rapid change)<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Play around with interval until the lines aren\u2019t too far apart nor too close<\/span><\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Density surface can show how values vary across a region<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">patterns in density surface are affected by distribution of sample points<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">May not actually be any features where highest density is<\/span><\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<ul>\n<li><b>Interpolation process- <\/b><span style=\"font-weight: 400\">generalizes and smooths the data so that extremely high\/low values may disappear<\/span><\/li>\n<\/ul>\n<ul>\n<li style=\"list-style-type: none\">\n<ul>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Makes patterns easier to see<\/span><\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<p><span style=\"font-weight: 400\">Mitchell- Chapter 5<\/span><\/p>\n<p><b>Why Map What\u2019s Inside?<\/b><\/p>\n<ul>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Monitor what\u2019s happening inside an area, or compare it to other areas<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Let\u2019s people compare areas to see where there\u2019s more or less of something<\/span><\/li>\n<\/ul>\n<p><b>Defining Your Analysis<\/b><\/p>\n<ul>\n<li style=\"list-style-type: none\">\n<ul>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Consider how many areas you have, what types of features you have inside the areas<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Single area:<\/span>\n<ul>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Service area around central facility<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Buffer that defines distance around some feature<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Administrative or natural boundary<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Area drawn manually<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Result of a model<\/span><\/li>\n<\/ul>\n<\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Multiple areas:<\/span><\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<ul>\n<li><b>Contiguous- <\/b><span style=\"font-weight: 400\">touching or adjacent<\/span><\/li>\n<\/ul>\n<ul>\n<li><b>Disjunct- <\/b><span style=\"font-weight: 400\">separated<\/span><\/li>\n<\/ul>\n<ul>\n<li><b>Nested<\/b><span style=\"font-weight: 400\">&#8211; areas within each other<\/span><\/li>\n<\/ul>\n<ul>\n<li><b>Discrete features- <\/b><span style=\"font-weight: 400\">distinct and identifiable<\/span><\/li>\n<\/ul>\n<ul>\n<li><b>Continuous features- <\/b><span style=\"font-weight: 400\">represent seamless geographical phenomena<\/span><\/li>\n<\/ul>\n<ul>\n<li style=\"list-style-type: none\">\n<ul>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Spatially continuous categories or classes<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Continuous values<\/span><\/li>\n<\/ul>\n<\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Do you need a list, count, or summary?<\/span>\n<ul>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">GIS can:<\/span>\n<ul>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Find out if feature is inside an area<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Find number of features in an area<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Get list of features in area<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Get summary of what\u2019s inside an area<\/span><\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Linear features and discrete areas might lie partially inside and outside an area (can choose whether or not to include these)<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">If you need list\/count of features include those partially in<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">If need to know amount of something in area only include those inside<\/span><\/li>\n<\/ul>\n<p><b>Three Ways of Finding What\u2019s Inside<\/b><\/p>\n<ul>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Drawing Areas and Features<\/span>\n<ul>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Create map showing boundary of area and the features<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Good visual approach to finding what is in an area<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Need dataset containing boundary area and dataset containing the features<\/span><\/li>\n<\/ul>\n<\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Selecting the features inside an area<\/span>\n<ul>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Specify area and layer containing features, GIS selects subset of features in area<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Gets list\/summary of features inside single area<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Need dataset of areas and dataset of features<\/span><\/li>\n<\/ul>\n<\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Overlaying the areas and features<\/span>\n<ul>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">GIS combines area and features to create new layer with attributes of both or compares two layers to calculate summary statistics<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Good for finding features in multiple areas or how much of something is in an area<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Need dataset of areas and dataset of features<\/span><\/li>\n<\/ul>\n<\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Overlay the areas and features if:<\/span>\n<ul>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Have multiple areas and want summary of what\u2019s inside<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Have single area and you need a list or summary of discrete features<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Have a single area and need summary of continuous values<\/span><\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<p><b>Drawing Areas and Features<\/b><\/p>\n<ul>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Key is to create map that makes it easy to see which features are inside the area<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Individual locations\/linear features can be drawn using single symbol (or symbolize by category\/quantity)<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Discrete areas:<\/span>\n<ul>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Shade the outer area with light color and draw boundaries of features on top (emphasizes features)<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Fill outer area with translucent color or a pattern on top of discrete area boundaries (emphasizes outer area)<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Draw outer area boundary with thick line and discrete area boundaries with thin line in lighter shade\/different color (use if shading discrete areas by category or class range)<\/span><\/li>\n<\/ul>\n<\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Use contrasting shades\/colors to distinguish areas<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">If graphing continuous data<\/span>\n<ul>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Draw areas symbolized by category or quantity<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Then draw boundary of areas on top<\/span><\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<p><b>Selecting Features Inside an Area<\/b><\/p>\n<ul>\n<li style=\"list-style-type: none\">\n<ul>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">With this, specify features and the area<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Can also find what\u2019s inside set of areas you\u2019re treating as one<\/span><\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<ul>\n<li><b>Geographic selection- <\/b><span style=\"font-weight: 400\">quick way to find out which features are within a given distance of another feature<\/span><\/li>\n<\/ul>\n<ul>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">If you have data summarized by area, can only summarize it using boundaries that fully enclose the area<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">GIS can create report of selected features or create statistical summary<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Common summaries:<\/span>\n<ul>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Count<\/span>\n<ul>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Total number of features inside area<\/span><\/li>\n<\/ul>\n<\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Frequency<\/span>\n<ul>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Number of features with a given value inside the area displayed as a table<\/span><\/li>\n<\/ul>\n<\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Summary of numeric attribute<\/span>\n<ul>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Sum- overall total or total by category<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Average- total of numeric attribute divided by number of features<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Median- value in middle range of values for an attribute<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Standard deviation- average amount values are from mean<\/span><\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Draw features inside area one color, outside area different lighter color<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Draw features inside based on attribute value and draw features outside single color<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Draw all features based on attribute value, but outside ones a lighter color<\/span><\/li>\n<\/ul>\n<p><b>Overlaying Areas and Features<\/b><\/p>\n<ul>\n<li style=\"list-style-type: none\">\n<ul>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Helps find which discrete features are inside which areas and summarize them<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">GIS tags each feature with a code for area it falls within and assigns the area\u2019s attributes to each feature<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Can get list of features or summary of attribute value by area<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">When line or area feature falls within two or more areas, GIS splits the feature where it crosses the boundary and builds new areas in a new dataset<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">If overlaying single area, can do same kind of analysis you would do with geographic selection<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">If overlaying several areas on set of features, can summarize features by area<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Can also summarize by category or value<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">If overlaying area on data summarized by area, make sure summarized area falls completely inside<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">If have single area, mapping individual locations similar to geographic selection<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">If mapping line or area features can just draw portion within the area<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Overlaying areas with continuous categories or classes<\/span>\n<ul>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">GIS summarizes how many of each category or class features fall inside one or more areas (can get map, table, or chart of results)<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Vector method<\/span>\n<ul>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">GIS splits category or class boundaries where they cross areas and creates a new dataset with the areas that result<\/span><\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<ul>\n<li><b>Slivers- <\/b><span style=\"font-weight: 400\">very small areas that are a result of overlaying areas on areas<\/span><\/li>\n<\/ul>\n<ul>\n<li style=\"list-style-type: none\">\n<ul>\n<li style=\"list-style-type: none\">\n<ul>\n<li style=\"list-style-type: none\">\n<ul>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Any areas with areal extent less than smallest area in either input dataset should be considered a sliver<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Consider accuracy of your data<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Good idea to only remove very small areas first then manually check any remaining small areas<\/span><\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Raster method<\/span>\n<ul>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">GIS compares each cell on area layer to the corresponding cell on layer containing the categories, counts number of cells of each category within each area, calculates areal extent, displays results in a table<\/span><\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Vector method provides more precise measure of areal extent but requires more processing<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">To display and analyze results you\u2019ll need a table that lists areal extent of each category (GIS creates this with raster overlay)<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">If looking at how much of each category is inside a single area, you can use table to create a bar chart showing amount of each category in an area<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">For multiple areas with a single category a simple bar chart will show how the areas compare<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">If multiple areas with multiple categories create a histogram showing multiple side-by-side bars (can also place pie\/bar chart in each area)<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">If you have a layer of continuous values, you can have GIS summarize the values and create a map or table of summary statistics<\/span>\n<ul>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Can create chart from the table to compare areas based on a particular statistic<\/span><\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<p><span style=\"font-weight: 400\">Mitchell- Chapter 6<\/span><\/p>\n<p><b>Why Map What\u2019s Nearby<\/b><\/p>\n<ul>\n<li style=\"list-style-type: none\">\n<ul>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Can find out what\u2019s happening within a set distance of a feature or find out what\u2019s in traveling range<\/span><\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<ul>\n<li><b>Traveling range<\/b><span style=\"font-weight: 400\">&#8211; range measured using distance, time, or cost<\/span><\/li>\n<\/ul>\n<p><b>Defining Your Analysis<\/b><\/p>\n<ul>\n<li style=\"list-style-type: none\">\n<ul>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Can measure straight-line distance, measure distance\/cost over a network, or measure cost over a surface<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Surrounding features may simply be within a source feature\u2019s area of influence (no movement between source and surrounding features)<\/span><\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<ul>\n<li><b>Area of influence- <\/b><span style=\"font-weight: 400\">usually measured using straight-line distance<\/span><\/li>\n<\/ul>\n<ul>\n<li style=\"list-style-type: none\">\n<ul>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">May also be movement or travel between source and surrounding features<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Can measure what\u2019s <\/span><b>nearby<\/b><span style=\"font-weight: 400\"> using distance or cost<\/span><\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<ul>\n<li><b>Travel costs- <\/b><span style=\"font-weight: 400\">time, money, and effort it takes to go somewhere<\/span><\/li>\n<\/ul>\n<ul>\n<li style=\"list-style-type: none\">\n<ul>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Decide whether you are measuring along flat surface (<\/span><b>planar method<\/b><span style=\"font-weight: 400\">) or along curve of Earth (<\/span><b>geodesic method<\/b><span style=\"font-weight: 400\">)<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Planar method is appropriate when area of interest is small, geodesic method when investigating large area<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Output layers made using geodesic method will be displayed correctly over curved surface of the globe<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">\\once you identify features near source you can get a list of the features, a count, or a summary statistic based on feature attribute<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Summary statistic can be<\/span>\n<ul>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Total amount<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Amount by category<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Statistical summary (average, minimum, maximum, standard deviation)<\/span><\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<ul>\n<li><b>Inclusive rings- <\/b><span style=\"font-weight: 400\">useful for finding out how the total amount increases as the distance increases<\/span><\/li>\n<\/ul>\n<ul>\n<li><b>Distinct bands- <\/b><span style=\"font-weight: 400\">useful if you want to compare distance to other characteristics<\/span><\/li>\n<\/ul>\n<p><b>Three Ways of Finding What\u2019s Nearby<\/b><\/p>\n<ul>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Straight-line distance<\/span>\n<ul>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Specify source feature and the distance, GIS finds area or the surrounding features within the distance<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Good for creating a boundary<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Use if defining area of influence or want quick travel range estimate<\/span><\/li>\n<\/ul>\n<\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Distance or Cost Over a Network<\/span>\n<ul>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Specify source locations and a distance or travel cost along each linear feature, GIS finds which segments of the network are within the distance or cost<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Good for finding what\u2019s within travel distance or cost of a location<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Use if measuring travel over a fixed infrastructure to or from a source<\/span><\/li>\n<\/ul>\n<\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Cost Over a Surface<\/span>\n<ul>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Specify the location of source features and a travel cost, GIS creates new layer showing the travel cost from each source feature<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Good for calculating overland travel cost<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Use if measuring overland travel<\/span><\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<p><b>Using Straight-Line Distance<\/b><\/p>\n<ul>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Create buffer to define a boundary and find what\u2019s inside<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Select features to find features within a given distance<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Calculate feature-to-feature distance to find and assign distance to locations near a source<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Create a distance surface to calculate continuous distance from a source<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Distance calculated from distance formula in math\/physics<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Creating a buffer<\/span>\n<ul>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Specify the source feature and buffer distance<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">With multiple features, Gis can create a buffer of equal or variable distance for each<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Can specify several source features and GIS will create buffer around all of them at once<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">To know how many features are within several distance ranges of a source as inclusive rings you need to create multiple buffers at each interval<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Show features like streets, administrative boundaries, water bodies, or other landmarks<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Map should also clearly label buffer distance<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Can select features within range of buffer, or can do multiple times for multiple distance ranges<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">To create map of features within buffer of source, put all features but make ones within buffer distance a different color<\/span><\/li>\n<\/ul>\n<\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Can go feature to feature and find each distance from the feature to the source<\/span>\n<ul>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Can put this info in a data table to analyze<\/span><\/li>\n<\/ul>\n<\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">You can specify maximum distance within which locations should be included<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Can use tags for each location to easily map what\u2019s within several distances of a source<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Options for point-to-point maps<\/span>\n<ul>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Surrounding locations color-coded by distance from source<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Surrounding locations color-coded by closest source<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Spider diagram<\/span>\n<ul>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Line drawn between each location and its source<\/span><\/li>\n<\/ul>\n<\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Source features using graduated point symbols<\/span><\/li>\n<\/ul>\n<\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Creating a Distance Surface<\/span>\n<ul>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Create raster layer of continuous distance from the source<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Creating distance ranges<\/span>\n<ul>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Display each cell using graduated colors either as continuous range or grouped into classes<\/span><\/li>\n<\/ul>\n<\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Can specify maximum distance to limit GIS when it calculates distances<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Need to create separate input layer for each source you plan on mapping<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">If mapping discrete features, place them atop distance surface (surface displayed using graduated colors)<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Continuous data stored as raster cannot be shown on top of distance surface<\/span>\n<ul>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">To show, combine reclassified distance surface with surrounding features<\/span><\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<p><b>Measuring Distance or Cost Over a Network<\/b><\/p>\n<ul>\n<li style=\"list-style-type: none\">\n<ul>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">GIS automatically identifies all lines in a network within given distance, time, or cost of source location<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">ArcGIS provides street network that is updated regularly<\/span><\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<ul>\n<li><b>Geometric layer- <\/b><span style=\"font-weight: 400\">composed of edges, lines, junctions, and turns<\/span><\/li>\n<\/ul>\n<ul>\n<li><b>Junctions<\/b><span style=\"font-weight: 400\">&#8211; points where edges meet<\/span><\/li>\n<\/ul>\n<ul>\n<li style=\"list-style-type: none\">\n<ul>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Street networks commonly used for finding what\u2019s nearby<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Travel time is one of most common costs<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">You can specify the cost for turns from one segment onto another or for stops at an intersection, can also limit which segments in a network can be travelled<\/span><\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<ul>\n<li><b>Turntable- <\/b><span style=\"font-weight: 400\">data table that lists the junctions for which you want to specify a cost<\/span><\/li>\n<\/ul>\n<ul>\n<li style=\"list-style-type: none\">\n<ul>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Can specify direction of travel along segments<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">If more than one center, GIS assigns segments to each concurrently<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Create a boundary in these cases<\/span>\n<ul>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Want list of individual locations<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Need count of locations in area covered by selected segments<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Have data summarized by area<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Need a list, count, or amount for linear features or areas<\/span><\/li>\n<\/ul>\n<\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Sum as you go in these cases<\/span>\n<ul>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Want a precise count of locations along network segments<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Don\u2019t need list of individual locations<\/span><\/li>\n<\/ul>\n<\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Can manually draw boundary or have GIS make it (compact or general)<\/span><\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<ul>\n<li><b>General boundary- <\/b><span style=\"font-weight: 400\">connects farthest reaches of selected segments<\/span><\/li>\n<\/ul>\n<ul>\n<li><b>Compact boundary-<\/b><span style=\"font-weight: 400\"> outlines the selected segments<\/span><\/li>\n<\/ul>\n<ul>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Can have GIS create distance rings to find what\u2019s within several distance or cost values<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Summing as you go<\/span>\n<ul>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">GIS sums counts or amounts as it searches outward from center along the network<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Can specify that GIS stops assigning streets once it reaches a maximum count or amount<\/span><\/li>\n<\/ul>\n<\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Once GIS finishes assigning segments it automatically shows the entire network and highlights selected segments<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Display center using symbol easily distinguishable from other locations<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Label centers<\/span><\/li>\n<\/ul>\n<p><b>Calculating Cost Over a Geographic Surface<\/b><\/p>\n<ul>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">GIS creates raster layer in which the value of each cell is the total travel cost from the nearest source cell<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Calculating cost over surface shows you rate of change<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Make sure to specify what cost is (time, money, distance, etc.)<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">To create cost layer based on single factor, reclassify an existing layer based on an attribute value<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">To create cost layer based on several factors, combine all the input layers<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Calculated value is assigned to entire area covered by the cell<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Larger the cell, more approximate the value for locations farther from the cell center<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Can modify cost distance by assigning maximum cost or using barriers to specify areas that are off-limits<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">Output layer is a surface of increasing cost values radiating outward from source<\/span><\/li>\n<li style=\"font-weight: 400\"><span style=\"font-weight: 400\">When mapping, show discrete features on top of cost distance surface (distance grid displayed using graduated colors)<\/span><\/li>\n<\/ul>\n","protected":false},"excerpt":{"rendered":"<p>Mitchell- Chapter 4 Why Mapping Density? Shows concentrations of features Good for overall patterns Density map uses uniform areal unit to show feature distributions Deciding What to Map Map density in one of two ways: Shading defined areas based on density values Create a density surface Mapping the density of points or lines is usually done using density surface Can map data already summarized by defined areas (ex: census tracts, forest districts, administrative boundaries) Can map density of features or of feature values Two Ways of Mapping Density Density map gives you density per area measurement By Defined Area: Dot density maps show density graphically, rather than showing density value To calculate density value for each area, divide total number of features by area of polygon Each area then shaded based on calculated value Can see areas of higher density but not centers of density Could also create shaded fill map By Density Surface: Density surface usually created in GIS as a raster layer Each cell gets density value based on number of features within radius of cell This provides more detailed info, but more effort Point data used to create density surface may be Locations of features Sample points you\u2019ve collected data for Can create density surfaces for individual locations or linear features Can also create contour map Mapping Density For Defined Areas Dot density map or calculated density for an area Calculating Density Value for Defined Areas: To do so, add new value for feature, then assign density value by dividing value being mapped by area of designated polygon Make sure units align Use range of shades of a couple hues Density treated as ratio and graphed like one ArcGIS lets you calculate density easily, but values are temporary and not stored in database Creating a Dot Density Map: Map each area based on total count\/amount and specify how much each dot represents GIS divides value of polygon by amount represented by a dot to find how many dots to draw in an area Give quick sense of density in a space Dots represent totals rather than calculated density values Specify dot value and size (don\u2019t be scared to play around) Display dots based on smaller areas, draw boundaries of larger areas That way boundaries won\u2019t obscure dots Creating a Density Surface Created in GIS raster layers (good for showing where point or line features are concentrated) To create density surface GIS: Defines a neighborhood (based on specified search radius) around each cell center Totals number of features in this neighborhood Divide number by area of neighborhood If using data value instead of features GIS: Totals that value for all features in neighborhood Divides that by area of neighborhood Parameters that affect how GIS calculates density Cell size Determines how coarse or fine patterns will appear (smaller cell size = smoother surface, but longer processing time and more storage space) Larger cell = faster processing but coarser surface In general, set cell size to have 10-100 cells per density unit To calculate cell size Convert density units to cell units Divide by number of cells per density unit Take square root of cell area to get length of one side Search Radius Larger the search radius the more generalized the patterns in the density surface will be (GIS also considers more features when calculating value of each cell) Smaller radius shows more local variation (be careful not to make too small or you\u2019ll lose broader patterns) Calculation Method Two Methods For Calculating Cell Values: Count features in search radius of each cell Result is a series of overlapping rings Weighted method Uses mathematical function to give more weight to values closer to center of cell Weighting drops off rapidly for features outside search radius Every cell in layer is counted and assigned a value Smoother, more generalized surface and easy-to-interpret patterns Units Choose a value for units that reflects features being mapped If areal units are different than cell units, legend values are extrapolated If you have data summarized by defined areas create a density surface: Use center points (centroids) of defined areas to create density surface based on value assigned to each area Do this to highlight patterns in the map with less emphasis on individual polygons Display density surface using either graduated colors or contours Graduated colors Classify unique density values for each cell to see patterns Create custom class ranges or specify standard classification scheme and let GIS create classes for you Classification schemes: Natural breaks&#8211; based on groupings of data values Quantile&#8211; each class same number of cells inside Equal interval&#8211; difference between high and low value the same for each class Standard Deviation&#8211; classes defined by number of standard deviations from mean of all values in layer GIS lets you specify number of classes to assign the density values Using a few classes highlights the areas with highest density but may not show subtleties in the patterns Density surfaces usually displayed using different shades of a single color If using standard deviation use shades of one color for values above mean, and shades of a different color for values below the mean Areas of higher value use darker colors Using Contours Contour lines connect points of equal density value on the surface Most GIS software makes contour lines automatically (just specify contour interval) Contours are good for showing rate of change across the surface (closer contours = more rapid change) Play around with interval until the lines aren\u2019t too far apart nor too close Density surface can show how values vary across a region patterns in density surface are affected by distribution of sample points May not actually be any features where highest density is Interpolation process- generalizes and smooths the data so that extremely high\/low values may disappear Makes patterns easier to see Mitchell- Chapter 5 Why Map What\u2019s Inside? Monitor what\u2019s happening inside an area, or compare it to other areas Let\u2019s people compare areas to see where there\u2019s more or less of something Defining Your Analysis Consider how many areas you have, what types of features you have inside the areas Single area: Service area around central facility Buffer that defines distance around some feature Administrative or natural boundary Area drawn manually Result of a model Multiple areas: Contiguous- touching or adjacent Disjunct- separated Nested&#8211; areas within each other Discrete features- distinct and identifiable Continuous features- represent seamless geographical phenomena Spatially continuous categories or classes Continuous values Do you need a list, count, or summary? GIS can: Find out if feature is inside an area Find number of features in an area Get list of features in area Get summary of what\u2019s inside an area Linear features and discrete areas might lie partially inside and outside an area (can choose whether or not to include these) If you need list\/count of features include those partially in If need to know amount of something in area only include those inside Three Ways of Finding What\u2019s Inside Drawing Areas and Features Create map showing boundary of area and the features Good visual approach to finding what is in an area Need dataset containing boundary area and dataset containing the features Selecting the features inside an area Specify area and layer containing features, GIS selects subset of features in area Gets list\/summary of features inside single area Need dataset of areas and dataset of features Overlaying the areas and features GIS combines area and features to create new layer with attributes of both or compares two layers to calculate summary statistics Good for finding features in multiple areas or how much of something is in an area Need dataset of areas and dataset of features Overlay the areas and features if: Have multiple areas and want summary of what\u2019s inside Have single area and you need a list or summary of discrete features Have a single area and need summary of continuous values Drawing Areas and Features Key is to create map that makes it easy to see which features are inside the area Individual locations\/linear features can be drawn using single symbol (or symbolize by category\/quantity) Discrete areas: Shade the outer area with light color and draw boundaries of features on top (emphasizes features) Fill outer area with translucent color or a pattern on top of discrete area boundaries (emphasizes outer area) Draw outer area boundary with thick line and discrete area boundaries with thin line in lighter shade\/different color (use if shading discrete areas by category or class range) Use contrasting shades\/colors to distinguish areas If graphing continuous data Draw areas symbolized by category or quantity Then draw boundary of areas on top Selecting Features Inside an Area With this, specify features and the area Can also find what\u2019s inside set of areas you\u2019re treating as one Geographic selection- quick way to find out which features are within a given distance of another feature If you have data summarized by area, can only summarize it using boundaries that fully enclose the area GIS can create report of selected features or create statistical summary Common summaries: Count Total number of features inside area Frequency Number of features with a given value inside the area displayed as a table Summary of numeric attribute Sum- overall total or total by category Average- total of numeric attribute divided by number of features Median- value in middle range of values for an attribute Standard deviation- average amount values are from mean Draw features inside area one color, outside area different lighter color Draw features inside based on attribute value and draw features outside single color Draw all features based on attribute value, but outside ones a lighter color Overlaying Areas and Features Helps find which discrete features are inside which areas and summarize them GIS tags each feature with a code for area it falls within and assigns the area\u2019s attributes to each feature Can get list of features or summary of attribute value by area When line or area feature falls within two or more areas, GIS splits the feature where it crosses the boundary and builds new areas in a new dataset If overlaying single area, can do same kind of analysis you would do with geographic selection If overlaying several areas on set of features, can summarize features by area Can also summarize by category or value If overlaying area on data summarized by area, make sure summarized area falls completely inside If have single area, mapping individual locations similar to geographic selection If mapping line or area features can just draw portion within the area Overlaying areas with continuous categories or classes GIS summarizes how many of each category or class features fall inside one or more areas (can get map, table, or chart of results) Vector method GIS splits category or class boundaries where they cross areas and creates a new dataset with the areas that result Slivers- very small areas that are a result of overlaying areas on areas Any areas with areal extent less than smallest area in either input dataset should be considered a sliver Consider accuracy of your data Good idea to only remove very small areas first then manually check any remaining small areas Raster method GIS compares each cell on area layer to the corresponding cell on layer containing the categories, counts number of cells of each category within each area, calculates areal extent, displays results in a table Vector method provides more precise measure of areal extent but requires more processing To display and analyze results you\u2019ll need a table that lists areal extent of each category (GIS creates this with raster overlay) If looking at how much of each category is inside a single area, you can use table to create a bar chart showing amount of each category in an area For multiple areas with a single category a simple bar chart will show how the areas compare If multiple areas with multiple categories create a histogram showing multiple side-by-side bars (can also place pie\/bar chart in each area) If you have a layer of continuous values, you can have GIS summarize the values and create a map or table of summary statistics Can create chart from the table to compare areas based on a particular statistic Mitchell- Chapter 6 Why Map What\u2019s Nearby Can find out what\u2019s happening within a set distance of a feature or find out what\u2019s in traveling range Traveling range&#8211; range measured using distance, time, or cost Defining Your Analysis Can measure straight-line distance, measure distance\/cost over a network, or measure cost over a surface Surrounding features may simply be within a source feature\u2019s area of influence (no movement between source and surrounding features) Area of influence- usually measured using straight-line distance May also be movement or travel between source and surrounding features Can measure what\u2019s nearby using distance or cost Travel costs- time, money, and effort it takes to go somewhere Decide whether you are measuring along flat surface (planar method) or along curve of Earth (geodesic method) Planar method is appropriate when area of interest is small, geodesic method when investigating large area Output layers made using geodesic method will be displayed correctly over curved surface of the globe \\once you identify features near source you can get a list of the features, a count, or a summary statistic based on feature attribute Summary statistic can be Total amount Amount by category Statistical summary (average, minimum, maximum, standard deviation) Inclusive rings- useful for finding out how the total amount increases as the distance increases Distinct bands- useful if you want to compare distance to other characteristics Three Ways of Finding What\u2019s Nearby Straight-line distance Specify source feature and the distance, GIS finds area or the surrounding features within the distance Good for creating a boundary Use if defining area of influence or want quick travel range estimate Distance or Cost Over a Network Specify source locations and a distance or travel cost along each linear feature, GIS finds which segments of the network are within the distance or cost Good for finding what\u2019s within travel distance or cost of a location Use if measuring travel over a fixed infrastructure to or from a source Cost Over a Surface Specify the location of source features and a travel cost, GIS creates new layer showing the travel cost from each source feature Good for calculating overland travel cost Use if measuring overland travel Using Straight-Line Distance Create buffer to define a boundary and find what\u2019s inside Select features to find features within a given distance Calculate feature-to-feature distance to find and assign distance to locations near a source Create a distance surface to calculate continuous distance from a source Distance calculated from distance formula in math\/physics Creating a buffer Specify the source feature and buffer distance With multiple features, Gis can create a buffer of equal or variable distance for each Can specify several source features and GIS will create buffer around all of them at once To know how many features are within several distance ranges of a source as inclusive rings you need to create multiple buffers at each interval Show features like streets, administrative boundaries, water bodies, or other landmarks Map should also clearly label buffer distance Can select features within range of buffer, or can do multiple times for multiple distance ranges To create map of features within buffer of source, put all features but make ones within buffer distance a different color Can go feature to feature and find each distance from the feature to the source Can put this info in a data table to analyze You can specify maximum distance within which locations should be included Can use tags for each location to easily map what\u2019s within several distances of a source Options for point-to-point maps Surrounding locations color-coded by distance from source Surrounding locations color-coded by closest source Spider diagram Line drawn between each location and its source Source features using graduated point symbols Creating a Distance Surface Create raster layer of continuous distance from the source Creating distance ranges Display each cell using graduated colors either as continuous range or grouped into classes Can specify maximum distance to limit GIS when it calculates distances Need to create separate input layer for each source you plan on mapping If mapping discrete features, place them atop distance surface (surface displayed using graduated colors) Continuous data stored as raster cannot be shown on top of distance surface To show, combine reclassified distance surface with surrounding features Measuring Distance or Cost Over a Network GIS automatically identifies all lines in a network within given distance, time, or cost of source location ArcGIS provides street network that is updated regularly Geometric layer- composed of edges, lines, junctions, and turns Junctions&#8211; points where edges meet Street networks commonly used for finding what\u2019s nearby Travel time is one of most common costs You can specify the cost for turns from one segment onto another or for stops at an intersection, can also limit which segments in a network can be travelled Turntable- data table that lists the junctions for which you want to specify a cost Can specify direction of travel along segments If more than one center, GIS assigns segments to each concurrently Create a boundary in these cases Want list of individual locations Need count of locations in area covered by selected segments Have data summarized by area Need a list, count, or amount for linear features or areas Sum as you go in these cases Want a precise count of locations along network segments Don\u2019t need list of individual locations Can manually draw boundary or have GIS make it (compact or general) General boundary- connects farthest reaches of selected segments Compact boundary- outlines the selected segments Can have GIS create distance rings to find what\u2019s within several distance or cost values Summing as you go GIS sums counts or amounts as it searches outward from center along the network Can specify that GIS stops assigning streets once it reaches a maximum count or amount Once GIS finishes assigning segments it automatically shows the entire network and highlights selected segments Display center using symbol easily distinguishable from other locations Label centers Calculating Cost Over a Geographic Surface GIS creates raster layer in which the value of each cell is the total travel cost from the nearest source cell Calculating cost over surface shows you rate of change Make sure to specify what cost is (time, money, distance, etc.) To create cost layer based on single factor, reclassify an existing layer based on an attribute value To create cost layer based on several factors, combine all the input layers Calculated value is assigned to entire area covered by the cell Larger the cell, more approximate the value for locations farther from the cell center Can modify cost distance by assigning maximum cost or using barriers to specify areas that are off-limits Output layer is a surface of increasing cost values radiating outward from source When mapping, show discrete features on top of cost distance surface (distance grid displayed using graduated colors)<\/p>\n","protected":false},"author":2331,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[4],"tags":[],"class_list":["post-5146","post","type-post","status-publish","format-standard","hentry","category-course-student-work"],"_links":{"self":[{"href":"https:\/\/sites.owu.edu\/geog-291\/wp-json\/wp\/v2\/posts\/5146","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/sites.owu.edu\/geog-291\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/sites.owu.edu\/geog-291\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/sites.owu.edu\/geog-291\/wp-json\/wp\/v2\/users\/2331"}],"replies":[{"embeddable":true,"href":"https:\/\/sites.owu.edu\/geog-291\/wp-json\/wp\/v2\/comments?post=5146"}],"version-history":[{"count":1,"href":"https:\/\/sites.owu.edu\/geog-291\/wp-json\/wp\/v2\/posts\/5146\/revisions"}],"predecessor-version":[{"id":5147,"href":"https:\/\/sites.owu.edu\/geog-291\/wp-json\/wp\/v2\/posts\/5146\/revisions\/5147"}],"wp:attachment":[{"href":"https:\/\/sites.owu.edu\/geog-291\/wp-json\/wp\/v2\/media?parent=5146"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/sites.owu.edu\/geog-291\/wp-json\/wp\/v2\/categories?post=5146"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/sites.owu.edu\/geog-291\/wp-json\/wp\/v2\/tags?post=5146"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}