Chapter 4:
- This chapter goes into detail about why you should map density and how to map it. Density mapping is used specifically when looking for patterns rather than individual features. There are two ways of mapping density, by defined area and by density surface. Using a defined area allows you to create a dot map, which means each dot represents a specified number of features. The density surface is created in GIS as a raster layer, which means each cell in the layer gets a density value that varies depending on what you are measuring. The use of color is also brought in again, when a part of the map has a higher density typically the color becomes darker to signify the amount. As someone who is not the best at math, I think learning how to calculate the correct density sizes seems to be important. The steps to this are to first convert density units to cell units, then divide by the number of cells, and then take the square root to get the cell size. Another important factor while mapping is your search radius. Having a large search radius generalizes the patterns of the density surface. You also need to specify your units, square meters can be used for something small but using it to track larger areas would not work. As we learned in previous chapters different classes need to be identified as they all have unique density values. Such as quantile having each class have the same number of cells. At the end of creating your density map know that the patterns you see depend on how the density surface was created. One cause of this was discussed earlier, which was having different search radiuses.
Chapter 5:
- This chapter is about mapping what is inside. It took me a little bit of reading to fully understand what this meant. Mapping what is inside means what is inside an area, so that if something occurs they can tell how close or if it is inside that area. Such as if someone was speeding in a school zone, they would suffer a harsher penalty. There are different methods for creating a boundary, and it depends on what you want to find. Some of the options to highlight are a service area, a buffer, a natural boundary, manually drawn territory, a floodplain, etc… You choose the barrier which also includes choosing if something that is partially in the barrier is included or not. Once the barrier is created you need a way of figuring out what is inside the barrier. You have to ask yourself what it is good for and what you need. To use this map you create a report in GIS of the selected features. Overlaying areas allows you to find the discrete areas and summarize them.
- Discrete: These are unique, identifiable features. You can list or count them. They are either locations, such as student addresses, crimes, or eagle nests. They can also be linear features.
- Continuous: Represents seamless geographic phenomena. It can include spatially continuous classes such as vegetation or elevation range.
- Continuous Values: Numeric values that vary continuously across a surface. They can be measures of temperature, elevation, or precipitation.
- Count: Total number of features inside and area.
- Frequency: The number of features with a given value is displayed as a table.
- Raster Method: Combining raster layers allows GIS to compare each cell on the layer with categories. It then calculates the areal extent and presents the results in a table. The areal extent causes this method to be the most efficient.
Chapter 6:
- This chapter goes into detail about mapping what is nearby, which is mapping within a set distance or travel range of a feature. It seems similar to mapping what is inside but mapping what is nearby lets you find out what is happening within a set distance of a feature. To find out what is nearby you can measure distance or cost over a network, or measure cost over a surface. Just like in the last chapter with creating a set boundary, you also have to determine what is considered nearby. I wouldn’t have thought to think about whether you are measuring over a flat plane or the curvature of the earth. I almost forgot that it can change the distance. There are three ways of measuring what is nearby, straight line distance, distance or cost over network, and cost over a surface. After choosing which way works, the next step is to create a buffer that can see what’s within the distance of the source. Sometimes I forget that a lot of this process is gathering and separating data and not yet creating a map. In this case, once you need to make a map you can choose to present what is inside the buffer or what is on both sides. There are other ways to make a map as well such as point-to-point distance, displaying what is near a source feature, color-coded, a spider diagram, and many more. The rest of the chapter is repetitive in its form, it guides you through a measuring form, what GIS does, and how to map it.
- Rings: Useful for finding out how the total amount increases as the distance increases
- Buffer: defines a boundary, multiple can be created at the same time
- Bands: Useful if you want to compare distance to other characteristics