Mitchell Chapter – 4 is about mapping density. This was mainly shown as population per county/census tract, or businesses per area. Mapping density is useful because it can be a way to display ratio data using either graduated colors, points or contour lines to visualize patterns. As an ecologist it could be useful to look at density maps showing percent logging or percent population in a given area so that I can find good study sites. The chapter covers different ways to display density on a map, and the main two methods are through points or density surface. When planning to map density it is important to think about what it is you are planning to use your map for. If you are planning to just try and visualize a trend and aren’t doing a lot of analysis from the map otherwise, it is best suited to use a large cell size. This is because a large cell generalizes your data, however it also processes a lot faster. It can be refined further to have a smaller cell size if further analysis is required.Â
Key words: Defined area density (density based on area of a polygon), Dot density (area mapped by count/amount and each dot is given an amount to represent), Cell size (amount of space that the GIS uses to represent data, smaller is more detailed but takes longer to process).
Mitchell Chapter – 5 is about what is actually represented by the map, and what it can be used to interpret. This can be done by designating an area surrounding a central point or by layering data on top of one another. This chapter also includes different ways to highlight different details about the map, such as by using just an outline of an area, an outline and shading the area, or by screening out the space around the area. Some applications for this that I can see, is by using census data to find out the amount of people living in poverty within a given area, this can be done by defining an area and than using graduated colors or symbols to show the count for the feature data within the defined space. A scientific application that I could use this for would be to map the land use types for a study area, say Delaware county, then I could define my specific study sites within the county and then use the land use map as a sort of base layer to determine what the land use type is for all of my given field sites.Â
Key words: Single area (area surrounding a central point), Count (total number of features in an area), Frequency (number of features within a given value or range of values inside the area).
Mitchell Chapter – 6 is about determining distance from a source. This is often expressed as a cost, whether that cost be time, money, or physical distance. To do so you need to define your area, by selecting either a line, network, or a surface. Measuring distance can sometimes be difficult as the earth is curved and depending on the scale of your area it is sometimes necessary to use the geodesic method to account for the earth’s curvature. A few things that can be done by measuring distance or cost induce: generating lists of customers near a given business to give advertisements to, counting the amount of properties near a fire station, or generating summary statistics around your area. A good use of concepts from this chapter would be buffering an area surrounding a tributary with vegetation and planning this out by selecting the tributary and then creating a buffer a set distance away from the tributary.Â
Key words: Inclusive rings (creates an area that is a specified distance away from a given point), Distance bands (similar to inclusive rings, but spanning distances incrementally), Straight line distance (the GIS defines an area based on a source feature and a given distance), Cost by Network (a travel cost is designated per each linear feature), Cost over a surface (Surface features of a specified area are given travel costs), Buffer (a zone is marked out a set distance away from a designated area), Spider diagram (lines are drawn connecting features back to a certain point they are close to)