Chapter 4
Chapter 4 talks about density(the number of things within a certain area/ volume) It talks about two ways to show density with the density by area model and the density by defined area or by surface. Density by defined area takes a distinguishable area(ex: county, zip code, etc) and collects the number of features and displays the area as a certain color based on the gradient number that the area has been given. Density by surface does not require defined borders and the range is editable. To find the density for either of these to find its range on the color coded gradient you must find the number of features and divide that by the area of which you are finding the density for.
I face some confusion about the representation of density through defined cells. Is the total map split up into equal cells and the number of the features counted and then the circle is placed in the middle of the cell or is the cell based off of the location of the features being studied(ex: businesses, employees, etc)Or does the GIS find the average distance between all points in the cell and move the circle to that point.
I enjoy that they often include what one particular map might be used for and by whom it might be used. It is good to have a clear explanation of how these techniques are used by everyday people and businesses.
Chapter 5
This chapter “finding what’s inside” had a focus on defined areas and how you can manipulate both their visual properties and informational properties to gain insight. The example of a flood plain was used a lot in this chapter to show how different areas can be overlaid with each other. You can take a group of defined areas(in the text it was personal properties categorized by their use) and overlay something like a floodplain or a watershed above the initial scape. You can also emphasize different parts of the map, for instance you can only include parts of the property area that are included in the flood plain area or you can have all properties with a part in the floodplain highlighted. The text makes it clear that this sort of mapping would be very important for things like watershed access, flooding, fire protection, school districts and more.
The text also made some comparative examples with drawing areas vs. Selecting the features inside the area. Drawing does not require any complex calculations so it is much easier to do but cannot list information so it is visual only. The other option selecting the features is good for knowing what is inside a group of areas but does not allow you to analyze areas individually. There is also the third option of overlay which lists multiple layers and allows you to draw conclusions based on which things overlay each other. The main drawback to this though is that it uses a lot of computational power.
An interesting question one might ask is how can these three methods be used together to make more meaningful conclusions?
Chapter 6
I think that it is an interesting idea to map the distance of something by cost. I wish you could do that in google maps to see how much you would need to spend on fuel.
This chapter analyzed the display of distance and how we show paths. A lot of the information seems like it would be tied to GPS but there was also some discussion of how it could be used by police stations, fire stations, etc… to understand their travel range. There was also discussion of the variable of cost which was a different way of looking at distance not in terms of location but in resources used to reach a point. I believe that this is a way to incorporate terrain changes into the mapping process.
There is also the sectioning of distances using inclusive rings which include all features from the outside to the center of the circle and distinct bands which are different distances from the center point and can indicate the number of features within a distinct distance band.
Another interesting style mentioned in the text was spider graphs which send a point straight to a feature within a certain range.
Switching from distance to cost creates a more detailed contour map because of the terrain features mapped.