Ch. 4
This chapter begins with map density and what it depicts. In simple terms, map density shows where high concentrations of a certain subject are. Paying attention to map density can help in observing patterns within an area to determine places of interest. Map density can also be shown in two different ways, being by area or density surface. The density by area maps are personally a little easier to understand. More dots or marks in a section of the map means there is a higher density of a certain feature there. Surface density doesn’t show much area separation, making it harder to work with to a degree (but it’s more accurate). With surface density, the GIS will determine the surface density for you, but the user has to determine the cell size. You have to be careful when determining the cell size because if it’s too big, the map may appear vague and unclear. Smaller cell sizes tend to have more detail, which in turn takes up a lot of storage space and may take longer to generate every detail. The textbook guides you through how to calculate an appropriate cell size based on the map size.
Ch. 5
Chapter 5 starts with explaining why it’s important to map things in the first place. Many different groups of people can utilize these maps for things like research and political demographics. For example, researchers tracking whale migration would want to see where individuals frequent for breedings and feeding, so marking these places and movements on a map proves to be useful to see where the whales prefer to be for certain reasons. It’s very important to label and define what’s inside the map so you don’t lose track of your data. The book gives a few different ways of finding and keeping track of features in the map, which consists of; drawing areas, selection inside an area, and overlaying areas. Drawing area only gives you a visual of where things are, but does not give you detailed information about what you’ve found. Selection allows you to actually specify the features in front of you. The GIS will search the area map for you and determine the feature and mark it. Overlaying will assign a code to a certain feature that’s in the area. The GIS will check the area for the specific feature and give the features IDs. Overlaying seems to be the most detailed and informative way of keeping track of features on your map.
Ch. 6
This last chapter gives reasons for why it’s significant to “map what’s nearby”. The three big methods the book gives for this is cost over surface, straight-line distance, and distance/cost over network. The straight-line distance is the simplest method of determining nearby features. This only measures the distance and roughly estimates the time it would take to reach a location. We use things like this a lot when we go places that are unfamiliar and need to know how to get there and the best (possibly shortest) route to get there. The cost over surface method allows us to determine the cost of travel to a destination. This requires more data to determine the cost involved, but the calculations prove to be pretty reliable. The last method is cost/distance over the network. This method combines the previous two, needing locations of interest along with the value/cost of an area. The last chunk of this chapter tells you how to calculate the cost (time, money, etc.) over a geographic surface. Once you add all of the layers to the map, the GIS thankfully calculates the total costs for you. Once that’s been done, the map user can filter through the cells of the map to pick out areas of higher or lower cost.