Mitchell Chapter 4:
This chapter begins with talking about map density and why it is important. Using a density map will allow you to see different features and high/low concentrations of features. You can use the GIS map in order to graph different points of data. There are two different types of mapping: 1) the density of features (like the locations of businesses) and 2) feature values (like the number of employees at each business). There are also two ways to map density, the first one being by the defined area, and the second being by the density surface.
The next section of the chapter compares the two methods of mapping, and allows people to see which method would be better for their data. I found this comparison very useful and something I will come back to! The next step of the mapping process is to calculate the actual density of the area being mapped. A dot map in particular gives people a really quick glance at the density and is very visual. I liked how the graph was portrayed in this. Specifically for a dot density map, they made sure to tell us that we have dots based on smaller areas, but the bigger boundaries would have to be defined.
I think it was interesting how they discussed calculating density values. It seems to me like they are just based on the cells and what values are in them. But I liked how they included the conversion and equations that would be helpful! The search radius allows for larger and more general patterns within the map. It lets you specifically put what data points you want to be calculated for density in there. Assigning the number of classes and using contours helps with creating the map, as discussed in Chapter 3. The chapter ends with learning about how to discuss your results!
Mitchell Chapter 5:
As the chapters have discussed, everyone uses GIS differently depending on their job. For example, the authors provided an example of how many drug-related arrests take place within a certain distance of a school, because that will enforce a bigger penalty. There are different types of boundaries you can draw as well. They also discuss how features can be discrete: unique, identifiable features; or continuous: seamless geographic phenomena. You also need to discover if you need a list, count, or summary based on your data. I think it’s cool that you can only choose features that are inside or outside your boundaries and not both, it makes it easier to comprehend.
However, Mitchell does go on to say that if you need information about what is beyond the area, then you can include that as well. There are three ways of finding out what is inside, and those three ways are: 1) drawing features and areas, 2) selecting the features inside the area, and 3) overlaying the areas and features. Similar to Chapter 4, I liked how they put in a little table of comparison on how to choose the different methods! This is very helpful to me. Making a map is the first step, and after that you have to follow the instructions based on what data you have. Discrete areas are important to note because the parcels inside can affect what is outside.
You can also specify features using geographic selection, which is finding out what features are in a particular distance of another feature. You can summarize using categories or quantities. The GIS will then select what features are inside the area and then flag the ones that are inside to let us know that they are inside. To read the results you can use the sum, the average/mean, the median, or the standard deviation. The final step is overlaying areas and features, and that seems like the coolest way to me! It will read the boundaries and make a map for us to examine the continuous categories or classes.
Mitchell Chapter 6:
While using GIS, you can find out what locations and features are nearby. Travelling ranges can include measuring distance, time, and cost, and that can be specific to a certain facility. However, to define a certain range, you can use one of three methods: 1) straight-line distance, 2) measure distance or cost over a network, or 3) the measure of cost over a surface. However, cost does not have to be an amount of money, it can also be measured in time. I thought that was interesting because I didn’t think about it that way! Like in Chapter 5, they talk about a list, count, and summary, and that is how it is defined.
The authors discuss how the different methods work, and what each method is specific for. Again, they provide a table that allows people to compare the best ways to use each method. If you have features that are within a given distance of a source feature, you should use a straight-line distance method. If you have to create other features in which you have to specify the buffer and source feature, then you create a buffer. It tells you how you can select and tag different features within the map. They also make different diagrams based on the data and also create a distance surface.
Summarizing discrete and continuous features depends on what data you have, and ArcGIS creates default displays that will do their own colors and features. I think it’s cool that you can specify the colors and boundaries that you want. The GIS will identify the lines in a network, and that will also help define the boundaries. Centers: “they usually represent centers that people, goods, or services travel to or from. You can then find the surrounding features along, or within, the area covered by those lines”. The map will start measuring at the center of your feature, then it will create the map around that and based on your boundaries. You can always make multiple centers too. The chapter ends with more ways to calculate data! It seems pretty easy as long as you’re thorough.