Jolliff Week 3

Chapter 4

Chapter 4 “Mapping Density” explains how mapping density allows you to see “patterns of where things are concentrated”. While some maps emphasize specific locations of features, Density maps focus on the patterns of certain features. I thought this was interesting because in the previous chapters we were looking at specific features, like individual crime scenes. With a density map it is more of a broad way of showing where for example the most crimes occur, and through this type of map you can see patterns of where the most crime is located or where there isn’t as much of a concentration of crimes occurring. Density maps can provide you with a density measurement per area. Raster layers are used to create density surfaces. Based on the reading the raster layers allow us to see concentrated features. I think if I’m understanding this correctly, you can have a cell of a map and if you take a radius around that cell you can figure out the  amount of features within that radius and that number is assigned to the cell and after you do that with all of the cells that is where you get your smoothed area of concentrations. Search radius can be large or small. Larger search radiuses show more generalized patterns, while smaller search radiuses show more local variation.

Chapter 5

I am having trouble understanding how all of these maps are different. I think they are different based on the features and also how the features are being analyzed. This chapter seems to be talking about what is going on in an area. You can monitor what’s happening this way, or you can use this information to compare different areas based on what is happening to them. They give the example of potentially mapping the affected area of a toxic plume. If not for this information appropriate action could be taken by the public or those with the ability to handle the situation. You can show boundaries of certain things such as buffers around streams, soil types in a parcel of land, and floodplains. I think that this is an interesting thing that I haven’t thought about before while looking at maps. On the topic of discrete or continuous features, discrete features are features that you can easily identify and they are unique. They are locations, addresses, crimes, etc. With continuous features you can summarize the features for each area.

Chapter6

In the chapter, Finding What’s Nearby, I learned that you can set distances and you can figure out what is going on within these distances of the certain feature you are looking at. You can label the nearness of a feature using distance or travel cost. I have gathered that it is important to know what information you will need because that will help you choose the best way to carry out your analysis. There are three ways of finding out what is nearby. Straight line distance, distance or cost over a network or, cost over a surface. Straight line distance is what you choose a specific source feature and the distance and then the area is found within the distance that you specified. When it comes to layers you need the source feature and then a layer with the distance to form what you are desiring. Straight line distance allows you to create boundaries around a source.  With Distance or cost over a network, I see this as when you put an address in your google maps and it shows you all of the routes and which one is the fastest. At least this is what I have gathered from the reading. Cost over a surface is when you have locations of source features and a travel cost. Adn from that “ “The GIS creates a new layer showing the travel cost from each source feature.” Cost over surface is more for overland travel, while cost or distance over a network is if you are traveling in fixed infrastructure. And for straight line distance this would be used for estimates of travel range.