Chapter 4
- Using density maps can be beneficial if you need to focus on identifying patterns or trends in comparison to other mapping methods that use the specific location of points of interest to gather information. Density also functions as a proportion, which can be helpful in comparing counties of different sizes or larger populations.
- A dot map is one way of mapping density. Each dot represents a set number of subject (ex. businesses) and the closer the dots are together the higher the density of the subjects in that area. This is an example of mapping density based on area, which is relatively easy but does not provide precise area about the centers of density. This method is useful if you already have data summarized by area.
- Another method of mapping density, creating a density surface, can be done in the form of a contour map. This method takes more data processing than the ‘density based on area’ method, but can also present a more precise view of the centers of the densities.
- One thing that stood out to me was that in dot density maps the dots don’t represent the actual location of the object. I assumed that the dots showed the location of each object and you could compare the density based on the object’s proximity to one another. According to the book, though, GIS places the dots randomly within the given area
- There are several factors that can affect legibility for both methods of mapping density. When using dot maps you can manipulate the size of the dots and how many dots are present (how many objects each dot represents). With the density surface method you can manipulate the cell size, search radius, calculation method, and units, which all can have a substantial impact on map appearance and effectiveness.
- When using graduated colors in a density surface map there are several ways to classify the different ‘levels’ of gradation: Natural breaks, quantile, equal interval, and standard deviation. The number of classifications can also impact the appearance of the map.
- Using contour lines is another way of showing density, as it connects points with the same value to create a line that indicates different levels of density.
Chapter 5
- The beginning of this chapter sort of answers a question I had earlier on in the reading (about what ‘inside’ could mean in the context of GIS). Considering ‘inside’ as in the confines of a boundary such as district or county makes much more sense.
- When looking at what’s mapped inside you should consider whether a feature is discrete or continuous; Discrete features can be given numerical values and are unique and identifiable. Discrete features can include locations or linear features. Continuous features are less definite in their boundaries and seamless in their transitions. Soil types, precipitation, and elevation are all examples of continuous features
- You can collect many different types of information from inside a given area depending on what you are looking for (ex. count, summary…). You can also determine whether to include objects/’parcels’ that are fully inside or partially inside the given area.
- There are three primary ways of finding what’s inside an area, each having their own pros, cons, and applications. These three methods are drawing the areas and features, selecting the features inside the area, or overlaying the areas and features. They can also all have a variation in the best way to display the results obtained that correlates to their most relevant function.
Chapter 6
- There are many apparent and practical uses for applying GIS to find what’s in a nearby area. There seems to be a theme of using GIS to search for objects that are within a given radius of something, in units such as travel time/cost or meters.
- It is often more beneficial to map nearby objects based on travel time than by distance, although it typically takes more preparation and data to map. The example provided of 3-minute travel time surrounding a fire department is a good way of showing this benefit; Travel time is more relevant to us in the instance of an emergency than distance, because travel time is the factor that we have to deal with and is what is actively being used as the unit of measurement when the service is dispatched.
- If mapping a large section you may want to consider the curvature of the Earth. In general, you should also keep in mind what you hope to get out of mapping, such as a list, count, or summary of information.
- There are three methods of determining what’s nearby: Using straight-line distance (is relatively simple but rough in approximation), distance or cost over a network (gives precise information and is used for measuring travel over a fixed infrastructure), and cost over a surface (used for determining how much area is within the travel range, which is measure by cost).
- Similarly to the different methods of mapping demonstrated in previous chapter, these three methods all can be presented in different manners. They serve seperate and often overlapping purposes. In designing a map or project it’s best that you select a method of determining what’s nearby that fits your specific project. This can include matching what information you hope to receive, the measurements you use to get this information, and how you want to present your findings.
- I think that all these different methods could be very overwhelming to learn at first, but once I have a specific idea of what kind of project I’d be applying these methods towards then it would be easier to select one.