Chapter 4
This chapter was all about mapping density. Mapping density can show different levels of concentration for specific features. This allows you to easily identify patterns in the data. You can use it for things like census maps and robberies per square mile. You can use GIS to map the density of certain points or lines. Both of these usually appear with some sort of density surface. You can map the amount of occurrences of a feature in a defined area or the values of said feature. You can create density maps based on features in two main ways; summarized by defined area or by creating a density surface. The first one is by defined area. This is a more graphical way of mapping density. You can use a dot map. These typically represent the density of individual locations. On a dot map, the closer the dots, the higher density for that feature in that specific location. To calculate a density value for each area, you divide the total number of features, or total value of the features, by the area of the polygon. The second method is by density surface. This is usually created in the GIS as a raster layer. Each area is assigned a density value based on the number of features with a radius of the area. This mode does take more effort but it provides a lot more detail than the former. Maps of this kind can show locations of features and continuous phenomena. To me personally. I think I like the sending area better. To me it just creates a better and easier to understand map. The cell size of either of these maps will determine the way the patterns. This is the one bad thing about these maps, if your cell size is wrong then you might see different patterns. It kind of reminds me of gerrymandering in a way. To find the cell size, convert the density units to cell units, divide by the cells and then take the square root to get the cell size on one side. This chapter was interesting to me. There’s a lot more that goes into density maps than I would have thought. Although when I’m actually working in the program this year I’ll probably need a textbook by me because it’s a lot of information to digest.
Chapter 5
This chapter was focused on mapping what was inside areas. This allows people to analyze data and decide what to do. One example that the book gives is a defense attorney can see if a crime was close to a school. In order to properly do this you need to know if you are looking at one or multiple areas, and what is in each. The chapter goes on to describe discrete and continuous phenomena and how you should map them. This was pretty similar to chapter 1. It’s sort of strange to me that some of this needs to be said, however, I wouldn’t think about it. It’s kind of crazy how many implications there are for GIS. I mean the book talks about all sorts of applications for it. So it makes sense that you would want to map inside the areas rather than just a feature area itself. You can also overlay multiple of these into different layers which would allow you to isolate certain points in certain areas. Continuous features usually are mapped as the bottom layer, with the defining area put on top of the phenomena. It’s somewhat hard to read but I think it’s a better alternative to the other way around. When selecting what points to put inside it’s best to think about the audience of the map. If you put in data that’s already being summarized by area, all you can do is put your border down on top of it. What’s really cool is that the GIS will actually help put together numerical data for you. This kind of makes me think about the idea of it being a quantitative tool. In my opinion, I think all maps should be accompanied by charts and graphs, this way it might help explain the map a little better.
Chapter 6
This chapter was all about finding what was around your feature. This way you know what kind of environment and people could be affected by the feature. This one actually sounds pretty cool. I do a lot of road trips and traveling, so this would be a cool thing to have so I could see what is around my hotel. In order to do this you would have to determine how far you want to measure. If you are looking for walkable places, you’re not going to measure what is 40 miles away from your hotel. The measure also doesn’t have to be a distance, it could also be the cost of traveling to a certain place. Or it could be the amount of gas needed to get to that place. Sometimes you have to worry about the curvature of the Earth. I never would really think that that is something I would have to worry about when making maps. There are 3 ways to find what’s nearby. The first way is using a straight-line distance. This will yield a radius around your feature in the shape of a circle. This is the one that I usually think about. The other is distance or cost over a network. With this one you specify the source locations and a distance or cost along a linear feature. You could map it using roads. The third way is cost over a surface. You specify the location of the source features and the travel costs. Then the GIS will make a layer showing that travel cost from each feature. Similar to the other types of maps you have to know who your audience is. Local people are not going to care too much about the nearest travel center. The GIS could also measure the difference between two features. If you are calculating distance for more than one source you can specify a max distance. This way you don’t get data points that you don’t care about. The cost of travel can also be represented as a continuous phenomena, which was really cool to me. This chapter was really cool to me. Similar to the last chapter they were talking about how useful the GIS can be, and it’s crazy how much it can honestly do.