Chapter 4 talks about mapping density. Mapping density shows you where the highest concentration of features are. It can be useful for looking at patterns rather than at the locations of individual features, and for mapping areas of different sizes. In order to map density you can shade areas based on density value. You can use GIS to map the density of points or lines. For lines. The density is usually based on length per unit area. There are different types of methods you can use. You can map density by area which is useful if you have data already summarized by area, or lines or points you can summarize. You can also create a density surface which is useful if you have individual locations, sample points or lines. Which method you want to use depends on what you have. In order to calculate density values you need cell size, search radius, calculation method and units. Cell size determines how smooth the surface is. If the cell size is smaller the surface will be smoother. If the cell size is large the surface will be more coarse. Search radius is also very important. The larger the search radius the more generalized the patterns in the density surface will be. There are two different
Chapter 5 talks about finding what’s inside. People map what’s inside an area to monitor what’s occurring inside or to compare several areas. You can draw an area boundary on top of the features to find what is inside. Geographic selection is also a quick way to see what features are within a given distance of another feature. If you have data that is already summarized by area you can only summarize it using boundaries that fully enclose the areas. You can also use GIS to create a report of selected features. You can also use GIS to create statistical summaries using the tools that are available with GIS. Statistics include average or mean, median, and standard deviation. You also want to create a map to see which features are inside in addition to statistics.
Chapter 6 talks about finding what’s nearby. You can use GIS to find out what is happening within a certain distance of a feature. Traveling range is measured using distance, time or cost which can help define the area served by a facility. Distance is one way of defining and measuring how close something is. But nearness doesn’t have to be measured using distance. You can also use cost to measure what’s nearby. You can use distance or cost to map what is nearby based on travel. For some analyses you can calculate the distance either assuming the earth is flat or taking into account the curvature of the earth. Once you have identified which features are near a source, you can get a list of features, a count, or summary statistic based on a feature attribute. An example of a list is the parcel ID and address of each lot within 300 feet of a road repair project. An example of count would be the total number of calls to 911 within a mile of a fire station. A summary statistic can either be a total amount such as the number of acres of land within a stream buffer, an amount by category or a statistical summary. To create a buffer you specify the source feature and the buffer distance. Once you create the buffer you can display it to see what’s within the distance of the source.