Chapter 4 gives us an insight into how mapping density can really create a map, as well as help viewers understand what topics are being presented. Mapping density can be very helpful due to the ways you can present it on a map. For example, the different shades on a map can help show how dense something is. Depending on what you are mapping, the patterns from the densities can be different. These differences help create more accurate areas on maps. Throughout the chapter, I was able to see the big differences between the dot density maps, the shaded density maps, and the more thermal-looking maps. There are definitely certain ones that are better to use than others; for example, if there were so many samples that you couldn’t see the data you are looking for, a dot map wouldn’t work (a shaded map would be better). One thing that really surprised me was that the larger the search radius, the more generalized the patterns in the density surface will be. For some reason, this just seems like it should be the opposite. I imagined that the smaller the area, the easier it would be to map and make it more general due to the fact that there isn’t going to be a lot of differences. After looking at the maps, though, that helped me understand why bigger is better for this type of map. Another important thing for maps is units. To make sure the map is proper, you have to have the right units to make it more specific to what data you are using.
Key Terms:
- Mapping Density: shows where the highest concentration of the feature is
- Two ways of mapping density:
- A defined area: by using something like a dot map, we can see how high densities are by the amount of dots (use for data already summarized by area)
- By density surface (use for individual locations, sample points, or lines)
- A dot density map: area based on a total count or amount and specified by how much each dot represents.
- Density Surface: good for showing where point or line features are concentrated.
- Higher density: darker marks
- Lower density: Lighter marks ( light maps)
Chapter 5 presents the ideas of what is actually inside a map, and why the information plotted is important. Making sure we map certain things in certain areas is important because it can help society grow and improve. One good thing about using different ways of mapping an area is that it can give you more information than you initially expected. If you were to draw a map a certain way, you could see the difference between the inside of the area and the outside of the area. One thing that is nice about GIS is that you get to decide the area and the layer containing the certain thing you are looking for, while GIS gives you a subset of features inside the area. One thing that I thought was cool was the overlapping features in areas. This is very useful as it can help you see the differences between inside your area and outside, which I was talking about before. It can help with finding features in several areas or also finding out how much of something is in an area. When making a map, it is good to ask yourself these questions. What it is good for, what types of features are you going to include, and what trade-offs are you getting from making this map. One thing that is good about this is that you can see from making an initial map if you need a single or multiple. In multiple areas, it can be hard to see certain things as well; to fix this, you can shade certain things you are looking for, or fill it with a pattern, or draw a boundary around the area. There are a lot of things to do, so it is nice to pick whatever will stick out the most to you.
Key Terms:
How to Analyze certain maps:
- Single Area:
- A service area around a central facility (fire response area)
- A buffer that defines a distance around some feature (a stream)
- An administrative or natural boundary (police beat, parcel of land)
- An area you draw manually (a proposed sales territory)
- Multiple Areas:
- Contiguous (zipcodes/watersheds)
- Disjunction (state parks)
- Discrete features: unique, identifiable features.
- Comparing methods:
- Drawing areas and features:
- What is it good for: finding out whether features are inside or outside an area.
- Types of features: locations, lines, areas, surfaces
- Trade-offs: quick and easy, but visual only, so you can’t get information about the features inside
- Selecting the features inside the area:
- What is it good for: getting a list or summary of features inside an area
- Types of features: locations, lines, and areas
- Trade-offs: good for getting info about what’s inside a single area, but does not tell you what’s in each of several areas (only all areas together)
- Overlaying the areas and features:
- What is it good for: finding out which features are inside which areas, and summarizing how many or how much by area
- Types of features: Locations, Lines, Areas. and Surfaces
- Trade-offs: Good for finding and displaying what’s within each of several areas, but requires more processing
- Drawing areas and features:
Chapter 6 helps explain how to see what is nearby in the maps that are created. GIS is helpful in letting us find out what is occurring within a set distance of a feature, as well as being able to find out what is within traveling range. Knowing what is within a travel range is good for helping to delineate areas that are suitable for a specific use. Some things that we use to see what is nearby are looking at straight-line distance, measuring distance or cost over a network, or measuring cost over a surface. When using the measurement of straight-line distance, that would be due to an area of influence. Before we are able to see what is near, we have to know other important aspects, which we talked about in past chapters. Each method for finding what is nearby is different, so when you are deciding which one to use, you need to look at what is being measured. If it is a quick estimate of travel range, then it would be straight-line distance. If you were measuring travel over a fixed infrastructure, then it would be cost or distance over a network. Finally, if you were to be measuring overland travel, then you would use cost over a surface, and all of these have their pros and cons. To use these techniques, you would have to use a buffer, and with this you can use as many buffers as you need to get all the features that should be in the map.
Key Terms:
- Traveling Range: is measured using distance, time, or cost
- The Planar Method: is appropriate when your area of interest is relatively small
- Inclusive Rings: are useful for finding out how the total amount increases as the distance increases
- Distinct Bands: are useful if you want to compare distance to other characteristics.
- Information that is needed from the analysis:
- Do you need a list, count, or summary?
- How many distance or cost ranges do you need?
- Three ways of finding what’s nearby:
- Straight-line distance
- Use for: Defining an area of influence around a feature, and creating a boundary or selecting features within the distance.
- Surrounding features: Locations, Lines, Areas
- Measure: Distance
- Pros: Relatively quick and easy
- Cons: Only gives a rough approximation of travel distance
- Cost over a surface
- Use for: Measuring overland travel and calculating how much area is within the travel range
- Surrounding features: continuous raster surface
- Measure: Cost
- Pros: Lets you combine several layers to measure overland travel cost
- Cons: Requires some data preparation to build the cost surface
- Distance or cost over a network
- Use for: measuring travel over a fixed infrastructure
- Surrounding features: Locations, Lines
- Measure: Distance or cost
- Pros: Gives more precise travel distance/cost over a network
- Cons: Requires an accurate network layer
- Straight-line distance
- Selecting features near several sources:
- First, select and tag features within the distance of the first source
- Secondly, select and tag the features within the distance of the second source
- Thirdly, select the features within the distance of both sources