Chapter 4 of the ESRI book is about the usage of density maps to find patterns among features and between different locations. Density maps are good for showing things like population per capita, and what a map represents changes when density is calculated. My immediate thought/comparison was that this is how elections are manipulated. Another way density can be altered is by mapping features or values within the features, which also changes what viewers will see. Mapping with dots shows the features themselves, and patterns can be found in the clusters of dots. Then you can add layers that show feature values, which could show different relationships than just what the dots represent. Another useful way to show density is to shade defined areas like counties or cities with lighter and darker tones to show the density of a feature or population within. Using dots, though, seems to be more useful for seeing patterns at a glance and is kind of aesthetically pleasing but looks like it requires a lot more messing with to get a good result. Then, there’s more explanation of making the raster layer around the dots, and finally a bit about using contours which looked a lot like a classic topographical map to me. Also, I’m not really sure how the centroids in defined areas work, or what the use of mapping them first is? I think that might have just been an image to show how the calculation is made. The chapter’s explanation of how different shapes and ways of layering discrete features helped me understand how shaded surfaces are useful, and they seem to work best in combination with other layers.
Key Terms:
-Defined areas
-Contours
-Density Values
Chapter 5 concerns mapping features and values inside of other shapes which can be defined loosely by the map maker, by natural boundaries, or administrative/county ones. Mapping what’s inside one area shows the viewer patterns within, but mapping features within multiple defined areas allows for the areas to be compared. Now, I’m starting to understand the usefulness of vectors vs. rasters and how rasters can be used for showing continuous values, classes, and categories, the latter being a classic elevation map and all three showing natural boundaries. Then you have to decide what in the area you want to analyze but once you decide that it seems like the program kind of figures it all out. Once again it seems pretty intuitive to anyone who’s ever told a computer what to do, you just have to decide what you want it to do. You can draw or select an area, or overlay another one to choose the area you want to examine. As with other methods, the one with the least drawbacks takes more time and processing power. For overlaying, it works well and looks nice to shade the area you are looking at, like a watershed, and then parcels and features under it. It’s then up to you to decide if you want to examine only entire parcels within the area or the parts of parcels that touch it.The examples here are where I really start to see the layering that was described in the first reading. GIS can then be used to calculate values within the chosen area. The section on overlaying features gets more in depth with this, and refers back to a lot of the density based calculations in the previous chapter.
Key Terms:
-Drawing
-Overlaying
Selecting
Chapter 6 is about mapping distances and objects surrounding a feature. Often, this is used for things like travel time. As someone without a car I think it would be interesting to map things like easiest bus routes to and from a location. The book mentions travel distance displayed in geometric patterns in things like roads, which would suit that perfectly, and mapping roads by travel times which could be adjusted for any form of transportation. An important choice here is the choice between showing distance from a feature or mapping out travel costs, and cost would be especially useful for bus riders. Then you once again have to choose an area and whether you need a list of parcels or features, a count, or a statistical summary. The area can be a straight line (radial) distance from a feature, a network of linear features like roads, or a continuous raster. The straight line doesn’t give any information about travel times, the network distance requires roads, and the raster requires more planning and data. Also, the concept of buffers around things like roads and streams might be a good use for one of my project ideas for 110. The chapter then goes back to the concept of ranges to make the data more understandable by using cost layers.I appreciated the note that cost can be money, time, or effort. That’s ART GIS, and the idea of layers and specifically a mask layer to remove areas from the data feels very photoshop coded to me. This might be a bit of a tangent and unimportant but the maps in this chapter were cool looking, and on that note with the program, I still appreciate that it does the hard math for you.
Key Terms:Â
-Straight Line Distance
-Network
-List, count, or summary