Chapter 4
Mapping density is crucial for maps, as it shows you where the highest concentration of a feature is. Density maps are also useful when observing patterns and mapping areas of different sizes. Using these maps allows you to measure the number of features with areal units (ex: hectares/square miles); this is a valuable feature so that distribution over area can be seen adequately. Density maps become very helpful when you are trying to map census tracts or countries since they vary in size.
To map density, you can shade areas based on density value, or you can create a density surface. Different density features can include locations of businesses, crimes, and numbers of employees.
Dots can be used to represent the density of the locations (specifically individual locations). The dots will represent a certain number of features (ex: one dot may be 2 birds). The closer together the dots are, the higher the density is.
To calculate the density: divide the total number of features by the area of the polygon
A density surface is created in the GIS and is created as a raster layer. A density surface can be made from individual locations or linear features (roads/streams).
Methods:
Make a density map by area if the data you have is already summarized by area.
Make a density surface if you have individual locations (sample points and lines).
Dot density map:
This is a map that uses dots to represent a total count or amount based on how much each dot represents
The dots don’t represent the actual locations
Used for quicker reads of the map
Represents density graphically
Cell size: determines how the patterns show on the maps.
Search radius: This affects how many patterns will show up on the maps.
Chapter 5
Single area: A single area makes it so you can monitor activity.
Buffer: defines a distance around a feature
Discrete features: are identifiable features (locations and linear features)
Overlaying areas and features creates a new layer that has the attributes of both of the layers. Overlaying can also be used to compare the two layers. This can be helpful when trying to find which features are in each of several areas or finding how much of a feature is in one or more areas. To do this, you need data within an area (a dataset with features) that includes all the attributes you want to summarize.
To see which areas are discrete, you can shade the outer area with a lighter color or draw the boundaries of that area’s features on top. By doing this, you can emphasize the features inside the area. Another option is filling out the outer area with a pattern or a translucent color. If you are shading discrete areas
To map a single area, you can shade the area in or use a thick line to show the boundary.
Count: the total number of features inside an area.
Frequency: the number of features that are in a given value.
Sum: the total number/overall total
Average: the total of a number divided by the number of features
Median: the value in the middle of the range
Standard deviation: the average amount of values
Raster method: this method combines raster layers. The GIS will compare each cell with the area layer that corresponds to the layer containing the categories. The number of cells is counted for each category within each area.
Chapter 6
This chapter how to find what happens within a distance on a map. It explains the importance of traveling range, how to define and measure what is near, and how to measure travel.
Traveling range: A measured distance (measured by space, time, and cost)
If you want to find what is nearby on the map, then you can calculate a straight-line distance. Or you can assess the cost over a net distance, or assess the cost across a surface. These are different methods that can be used. Sometimes the features that surround a certain area may already be within the area of influence.
Distance is used to know how close something is to another thing. To find what is nearby, you can use cost. A common cost is time, and time can be used to find what is nearby. An example would be that it takes longer for a customer to get to a store because bad weather impacts traffic. When considering travel, you can map what is nearby by distance or cost. The most accurate way to do this is to map travel costs.
Inclusive rings: Circles that encapsulate a certain distance
Spider diagram: looks like a spider; the GIS draws lines to two or more sources with a similar location
Distance surface: used to make buffers at specific distances