Chapter 4
The fourth chapter of Mitchell was about mapping the density of features. I found this chapter of Mitchell particularly intriguing because I have an interest in density maps. I find these types of maps interesting because they are typically each to read and the reader is able to get a lot of information at a glance. According to Mitchell, a density map âshows you where the highest concentration of features is.â The chapter describes two ways that density is able to be mapped, defined area and density surface. When creating a density map by defined area, a dot map is easily used. With a dot map, dots are able to represent the density of a thing within a location summarized by defined areas. These maps lean more towards showing the data graphically instead of density features. When creating a density map by density surface, a GIS raster layer is typically used. Each of the cells within the layer is assigned a density value. When using this method, the result is usually a density surface or a contour map. This method is typically a lot more labor and time-intensive. When comparing the two methods, it is easy to point out when one method should be used over the other. A density map should be created by a defined area when the data is already summarized by area or can be summarized. A density map should be created by density surface if the data consists of individual locations, sample points, or lines. This type of mapping is best used if the mapper is trying to see the concentration of a point. One comment I have for this chapter is that Mitchell introduces the idea of a raster layer while describing creating a density map by density surface, however, he doesnât explain what a raster layer is until later in the chapter. I feel like not knowing what a raster layer was until pages later caused me to struggle with the concept of density surface at first.
Chapter 5
The fifth chapter of Mitchell was about finding what is inside of a dedicated area of a map. Mitchell states that mapping the inside âlet(s) you see whether an activity occurs inside an area or summarize information for each of several areas so you can compare them.â He then gives two reasons for why someone might want to do this: to show whether or not to take action on something and to see if there is more or less of something. Personally, I like how this chapter was laid out. The format of this chapter was like chapter three with headings appearing as questions to help the reader. The chapter focuses on the three main methods to map what’s inside of a dedicated area. In the beginning, it tells the reader what things to consider in order to find the best method for them. The things listed to consider are as follows, the data you want to collect, whether you want to map a single area or multiple areas, whether your features are discrete or continuous, the information you want to find out from mapping, and if you are using features inside the area or both inside and partially outside the area. Next, the chapter then gives a brief description of the three main types of methods for mapping inside. First, there is
drawing areas and features, where the person creating the map will make the map to have it show the boundary of the area and the features inside of it. Next, there is selecting the features inside the area. The person creating the map will dedicate an area and the layer containing the features, and then GIS will select a subset of the features within the area. The final method is overlaying the areas and features. The person creating the map will combine the area and features in a new layer along with attributes for both or they will create two layers in order to calculate summary stats. After the brief description of the methods, the chapter then dives into greater detail by comparing the methods and walking the reader through how to create them.
Chapter 6
The sixth chapter of Mitchell is about finding what is nearby. Mitchell states that âfinding whatâs nearby lets you see whatâs within a set distance or travel range of a feature. This lets you monitor events in an area, or find the area served by a facility or the features affected by an activity.â One thing I found interesting in this chapter is the concept of costs. Cost is a way that you are able to measure distance while mapping. Measuring cost doesnât necessarily mean that it costs a certain amount of money to get there, which is what I originally thought when the concept was introduced. A cost is sort of like a trade off. While a cost can be the expense it will take to get to a certain point, it also can have other meanings. For instance, according to Mitchell, a cost is time and effort expended. These types of costs are called travel costs. When time is a cost, it means that it will take you an increased amount of time to get somewhere by taking a certain route. According to Mitchell, an example of time being a travel cost is âit takes longer ⌠for customers to get to a store through heavy traffic.â When effort expended is a cost, it is the wage of difficulty taken to get somewhere. An example given by Mitchell of effort expended is âa deer walking through thick underbrush versus open forest to reach a stream.â The concept of costs is so interesting to me because I never would have considered that these types of ideas would be used when mapping. I think that it is cool that as a mapper, you have to think about the different trade offs people will have to make while traveling a specific route.