Chapter 4:
Chapter 4 discusses how to map density. Mapping density is important to show the concentration of features and their patterns. For density, the number features are measured in uniform areal units. As with other GIS methods, careful consideration must be taken when deciding what to map. You have to consider if the data is plots, lines, or data summarized by data. You also have to consider whether you are mapping features or feature values. There are two main ways of mapping density, mapping by a defined area and mapping by a density surface. When mapping by a defined area density of individual features summarized by defined areas and each dot represents a set number. It doesn’t represent the exact location, but it’s easier to read than having one dot per location. When mapping by defined area density is calculated using the areal extent of each polygon. Dot maps are often used for mapping by defined area. They are based on the total count and how much each dot represents. There are several factors to keep in mind when making dot maps, like dot size, how much each dot represents, and area size. When mapping by density surface, raster layers are used and the total of features are divided by area. These maps offer more detailed information but require more effort. When deciding how to display the map it is important to consider aspects like cell size and search radius. These factors are important for making sure that the data is displayed in a way to properly display the patterns. The colors used for classes and how the breaks for classes are assigned. This chapter was helpful for understanding how to map density and the uses of it. There were a few points in this chapter where I struggled to understand the technical stuff, so I hope things will become more clear when actually using the GIS.
Chapter 5:
In chapter 5, the concept of “mapping what’s inside” is discussed. Mapping what is inside of a determined area is useful for monitoring what’s occurring inside it or to compare what’s inside several areas. There are several questions that need to be answered before deciding how to go about mapping. Are you finding what’s inside a single area or several? A single area lets you monitor activity or summarize information, while several areas lets you compare areas. Are the features inside discrete or continuous? Discrete features can be counted, listed, or summarized, while continuous features can be summarized. Do you need a list, count, or summary? The data needed is different if you want to get a list of all features, a total number of features or a summary of what’s inside of an area. Do you need to see the features that are completely or partially inside the area? Linear and discrete features may lie partially inside and outside of an area, so you must decide what to do in these situations. There are three ways to map what’s inside of an area. These include drawing areas and features, selecting features inside an area, and overlaying the areas and features. For drawing areas and features are drawn on top of features, which is good for seeing whether one or a few features are in an area. When selecting features inside an area you specify the area and the layer containing the features and selects a subset of features in the area, which is good for getting a list or summary of features in an area. When overlaying the areas and features the GIS creates a new layer with the attributes of area and features, which is good for finding which features are in each of several areas or how much of a feature is in one or more areas. This chapter did a good job at explaining what it means to map what’s inside an area.
Chapter 6:
Chapter 6 discussed the concept of mapping what is nearby a location. When mapping what is nearby, you can find out what is occurring within a set distance of a feature, identify what’s affected by an event or activity, and understand the cost of travel. The cost can be in regards to distance, time, monetary loss, effort, or other costs. As it seems to be a common occurrence with this book, the chapter discussed questions that you must ask yourself before you begin mapping. Is what’s nearby defined by a set distance or by travel to or from a feature? You should measure surrounding features using straight lines for distance or a geometric network using road data for travel. Are you measuring what’s nearby using distance or cost? Measuring by distance or cost can change the result significantly in some cases. Are you measuring distance over a flat plane or using the curvature of the earth? You should use the curvature of the earth for large areas. Do you need a list, count, or summary? It is important to understand what kind of data you need to achieve your desired map. How many distance or cost ranges do you need? You could have one range, inclusive rings, or district bands. The three ways to map what’s near a location are straight-line distance, distance or cost over a network or cost over a surface. When mapping straight line distance you specify the feature and distance and the GIS finds the area or features within the distance. This method is good for creating boundaries or selecting features at a set difference. When mapping distance or cost over a network you specify source location and distance/cost along a linear feature (like roads) and the GIS finds segments within distance/cost. This method is good for finding what’s within a distance/cost of a location. When mapping cost over surface you specify location and travel cost and the GIS creates a layer showing travel cost from feature. This method is good for calculating overland travel cost. Overall, I feel like this chapter thoroughly explained the concepts of mapping what is nearby a location and how it can be used. There were also some connections made to chapter 5, which I found helpful.
