Chapter 4:
Concepts & Definitions
- Mapping density: shows where the highest concentration of features is
- Defined area: mapping density graphically, using a dot map, or calculating a density value for each area
- Density surface: Created in GIS as a raster layer, each cell in layer has a density value
- Cell size: how coarse or fine patterns will appear, smaller cell size = smoother surface but more cells which will require more processing and storage space; larger cell size faster but more coarser surface and subtle patterns may not be noticed
- Search radius: larger search radius = more generalized patterns in the density surface
- Contour lines: connect points of equal density value on the surface
Notes
- Density maps are useful for looking at patterns more than locations of single features
- Density map shows the measure of number of features using a uniform aerial unit to clearly see distribution
- Mapping density useful for mapping areas like counties
- Dot maps can be an easy way to read a map if they are distributed throughout a defined area
- Density surface requires a lot of effort but gives the most detailed
- Density by a defined area is usually a shaded map, using multiple color shades
- Dot maps can give a quicker sense of density in a place
- Dots can be any amount of value 1 vs 100 vs 1000 units
- When creating a density surface, GIS will define a neighborhood around each cell center and then will automatically total the number of features that fall within it and assign that value to the cell
- Cells are square
- Converting density units to cell units: 1 sq. km = 1000m * 1000m = 1 million sq. m: 1 million sq. meters / 100 cells = 10,000 sq. meters per cell; sqrt 10,000 m = 100 m (one side of cell)
- GIS lets you specify the areal units for density values calculated, like square meters for wildlife animals
- Can display a density surface using graduated colors
Chapter 5:
Concepts & Definitions
- Single Area: A defined singular area to monitor activity/summarize information in it
- Multiple Areas: Like single area but looking at several of them to compare them
- Continuous values: numeric values that vary across a surface; temp, elevation, etc..
- Count: Total number of features inside an area; number of fast food in a county
- Frequency: Number of features with a given value/range of values, inside an area and displayed as a table, bar chart, or pie chart
- Sum: Overall total
- Average/Mean: Total numeric attribute divided by number of features
- Median: Value in middle of a range of values of an attribute
- Standard Deviation: Average amount values away from the mean
Notes
- Data should consider how many areas you have, and type of features inside them
- Discrete features unique and identifiable (like locations or crimes)
- Continuous features represent geographic phenomena
- Can use GIS to find out whether a feature is within an area
- Can create a boundary for linear features and discrete areas that may fall outside of a chosen area
- Can create a map showing the boundary of an area and features, good for seeing a few features inside/outside a single area; would just need data
- GIS can combine area and features to create a new layer with attributes to compare two layers
- Can symbolize locations or linear features with a single symbol or by category/quantity
- If mapping continuous data (soils or elevation), draw areas by category/quantity and then draw a boundary to highlight it
- Geographic selection is a way to find out which features are within a certain distance of another feature
- Overlaying areas and features can let you find which discrete features are within areas and summarize them
- GIS splits category/class boundaries where they cross areas and creates a new dataset within the areas that result
- Can use GIS to summarize the values and create a map/table of summary stats for each area
Chapter 6:
Concepts & Definitions
- Geodesic Method: Measuring distance using curvature of the earth
- Inclusive RIngs: Useful for finding how the total amount increases as the distance increases; like the total number of chicken diners within 1 mile versus 2 miles versus 10! Miles
- Distinct Bands: Used to compare distance to other characteristics, kind of like a range; number of beef stew shops between 1 miles and 2 miles
- Straight line distance: Can specify the source feature and distance and GIS will find the area/surrounding features within that distance
- Spider Diagram: GIS draws a line between each location and nearest source; useful for comparing patterns between multiple sources
- Graduated Symbols: Symbols used for comparing course features based on quantity; symbols = number of locations near a source feature
Notes
- Using GIS can tell you what’s occurring in a set distance of a feature and traveling range
- To find stuffy nearby, can measure using a straight line distance
- To define ‘nearby’, can be based on a set distance specified or travel to from feature to another; can also include travel cost
- Time would be an example of a cost, like going from a heavy traffic area to a store
- Effort could also be a type of travel cost; effort for a fish to swim upstream
- For measuring distance, have to consider if it’s a flat plane or use the curvature of the earth; small areas distances should be flat plane, larger should be done using the geodesic method
- Can specify the source locations and distance along a linear feature
- To create a buffer, specify source feature and then the buffer distance, GIS will draw a line and circle around the desired distance; can have different sizes of buffers around different features
- Can create distance ranges, each cell can have that unique value and can then display that value using colors
- Can create a boundary manually by drawing a line around selected segments or have GIS create the boundary; manually drawing boundaries give more flexibility but may take more time