Chapter 4: Mapping Density
This chapter first starts out with saying why mapping density is important. It’s important because it shows where the highest concentration of things is. This makes it easier to find areas that need help or just to see where a lot of buildings or places are in that area. Mapping density is useful especially for censuses or counties. Like every other thing being mapped, you have to decide what features you want to map and then get into even more detail by mapping feature values. You can also create a density surface from locations or singular things like a street. It says density surfaces are created in GIS as raster layers. A raster layer in one definition is described as a background layer for other layers.
Mapping density for defined areas:
You can map it in two ways: by a dot density map or by calculating density value for each area and shade each by value. The maps are usually two colors and shaded in. For density for defined areas, it’s treated and mapped like a ratio. Dot density maps are represented for a certain quantity. For example, one dot could equal 200 people. I think both types of maps are somewhat common and very easy to understand. In GIS terms of how all of this works when creating a density surface, GIS will find a neighborhood and add up all of its features. It then divides that by the area of the neighborhood. The value is then given to that neighborhood area. The GIS is essentially creating an average for every neighborhood and its area. The search radius can change. The cell size also matters. The smaller the cell, the smoother it is and the bigger it is the rougher or more coarse it will be.
Chapter 5: Finding What’s Inside
Mapping what is inside an area is really important for several reasons. For one, it lets people compare areas to see what there’s more of and what there’s less of. For example, mapping burglaries and where they occur may help police where to spend more time. Or, if you want to know where to put a police station, you will be able to map inside areas and see where police presence is needed. To do this you draw a boundary circle around a place. In this example, a circle is drawn around a fire station with all incidents including gas leaks, fire, medical and more. This makes it a layered map. Features here can be discrete (features you can count or list) or continuous (features like elevation). GIS can tell you if a singular feature is inside an area, list all the features, the number of features, and more. As I am learning, Geographic information systems can do a lot of things that we do not know about. This system is very intricate and useful in many different ways that I probably can’t comprehend. This article is super helpful because it gives plenty of examples and plenty of pictures or maps explaining. They also answer every question a person would have when learning about this technology. For example, when a feature falls out of a boundary line or area, it gives you the option to pick what you want to include or not. You can choose to exclude a feature but I think the best feature is choosing to keep a feature even if it runs outside of the boundary line. Three ways of finding what’s inside. The three are drawing areas and features, picking the features, and finally overlaying the areas and its features. Every method has its own advantages and disadvantages so it’s probably a preference. I think I would draw the areas and its features because it seems the easiest to understand and complete.
Chapter 6: Finding what’s Nearby:
The point of mapping what’s nearby is because you can find out what’s happening within a set distance of a feature affected by an event, store, or something else. The example they gave for this is that a city planner would have to let the residents around it know that they were building a beverage store. This identifies the area and the features. Also you can find out what’s in the traveling range. Finding this out can help define an area served by a facility or place. The example they gave for this is that a fire chief would want to know which streets are reachable in 3 minutes. Nearby is a word that everybody describes differently which makes this a little trickier than others. Depending on how you define it, it’ll tell you what method is most useful for you. The three main methods used are straight-line distance, distance or cost over a network, and cost over a surface. Just like for mapping what’s inside, every method has its own advantages and disadvantages. Straight line is used if you’re defining an area of influence or a quick estimate of travel range.You can create a buffer, you do this by specifying the source feature and buffer the distance. You pick features to find features within a given distance. With travel range or distance you have to factor in cost. Use distance or cost when you are measuring travel over a fixed infrastructure. Finally, use cost over surface if measuring overland travel. This chapter is word heavy so I know I had to reread some parts several times and I know I will probably have to go back and reread again! Like mentioned earlier, with travel, a cost will have to be calculated. For this, GIS creates a raster layer in which the value of each cell is the total cost from the nearest cell source. This seems easy enough seeing as if it was explained in the earlier chapter.