Chapter 4 talked about map density and its variables and when it is important to use it. I found it helpful the way it broke down what to map using density, the two ways of mapping density, mapping density concerning defined areas, and creating a density surface. The book talks about how density maps are useful when looking at patterns rather than locations of individual features and gives you a measurement of density per area, so comparing areas is done more accurately. Deciding what to map can be tricky though because density maps may not be useful in certain situations. I liked how the reading brought up that you should think about the features you are mapping and the information you need from the map before making the map itself. A concept I thought was interesting was the difference between map features and feature values. A map feature could be an example of locations of businesses where feature values could be the number of employees at each business. This distinction was helpful when thinking about the purpose of the map you are making. Mapping density by area is useful when you have data or lines or points that can be summarized by area resulting in a shaded fill map or dot density map. This is an easy process but is not as precise especially for large areas. Creating a density surface is useful when you have individual locations, sample points, or lines resulting in a shaded density surface or a contour map. This requires more data processing but can give a more accurate view of the centers of density. It was interesting to see how GIS plays a role in creating a density surface to make a running average of features per area resulting in a smoothed surface.
Chapter 5 discussed mapping what is inside an area to see what is happening there compared to other areas in order to see where there is more or less of something. The book goes into explaining the three ways of finding data for the inside of an area; drawing areas and features, selecting the features inside an area, and overlaying areas and features. Drawing areas and features create maps showing boundaries that can be used to see which features are inside and outside a specific area. This approach can show and use locations, lines, areas, and surfaces. Another way to find data is by selecting the features inside that area to get a list or summary of features inside an area or within a given distance of a feature. This approach shows locations, lines, and areas to get information about what is inside a single area rather than information about what is in each of several areas. The last way of finding data for the inside of an area is overlaying the areas and features to find out which features are in which areas, to give a summary of how many by area. Areas and features are combined through GIS to create a new layer showing attributes of both where they can be compared to calculate summary statistics for each area. This approach uses locations, lines, areas, and surfaces making this way good for displaying what is in each of the areas, but it does require more processing.Â
Chapter 6 discusses mapping data within a set distance to identify the area and features inside that area that are affected by an event or activity. This approach is effective in finding what is within a set distance to monitor activity in the area. Throughout the reading of this book, I have noticed how helpful the examples are that it gives. One example was a state forester monitoring logging that could use this method to make sure logging does not occur within a 100-meter distance from streams. This chapter also goes into detail about how to define your analysis, the three approaches to this method, using a straight-line distance, measuring distance or cost over a network, and calculating cost over a geographic area. To define your analysis there are three ways to get an accurate measure of what is nearby. This includes using straight-line distance to create a boundary or selecting features within the distance around a source. This is a pretty quick and easy approach but it can only give a rough estimate of travel distance. Measuring travel distance or cost of a location over a fixed infrastructure is achieved through GIS finding segments of the network that are within the distance or cost. This approach gives a more precise measurement over a network but requires an accurate network layer. Looking at costs over a surface is another method that can measure overland travel and calculate how much is within the travel distance. This allows for combining several layers to measure over-land travel costs but requires more data preparation to build the cost surface.Â