Wagner- Week 3

Chapter 4

The first section asked the question: why map density? Mapping density will show the concentration of features on a map. It is helpful when searching for a pattern rather than specific locations of features. Density maps use areal units that will clearly show the distribution.  The next section is on deciding what to map. You need to think about the features you’re mapping and the information you need from the map. If you want to map the density of points or lines you will typically use a density surface. If you have data that has already been summarized then you map it using defined areas.You also need to decide if you want to map features or the feature values because it can affect the patterns in the data. Section 3 focuses on the two ways of mapping density: based on features summarized by a defined area or by creating a density surface. When mapping by a defined area you can map density graphically, using a dot map, or by calculating a density value for each area. A density surface is created as a raster layer and each cell in the layer gets a density value. It then focuses on mapping density for defined areas. You can calculate a density value for defined areas based on the areal extent of each polygon or you can create a dot density map based on the total count or amount and then specify how much each dot represents. The last section is about creating a density surface. You will specify call size, search radius, calculation method, and units, all which affect how the GIS calculates the density. The cell size determines how coarse or fine the patterns appear and the search radius will determine how generalized the patterns will be, there are two calculation methods, and you can specify what kind of areal units you want the density to be calculated in. You can also display a density surface using either graduated colors or contours. 

Chapter 5

Chapter 5 was about finding what’s inside.  It is useful to map what’s inside an area to see what is happening there or to compare it to other insides of areas. You first need to determine if you are finding what’s inside a single area or each of many areas, if the features are continuous or discrete, what kind of information you need from the analysis, and if you need to see features that are completely or partially inside. What I have noticed is that there are always a lot of beginning steps and decisions when it comes to deciding how to map and analyze. You can find what’s inside by drawing areas and features, selecting the features inside the area, or overlaying the areas and features. By drawing areas and features you can simply look at what features are inside or outside the area. You can see which discrete and continuous features are inside the areas depending on what data you have. When you select features inside the area the GIS checks if each feature is inside the area and then flags the ones that are. Overlaying areas and features is more complex and finds which discrete features are inside certain areas and summarizes them, calculates the amount of each continuous category or class inside one or more areas, or summarizes continuous values inside one or more areas. Reading about all of these methods feels confusing and I think I would need to do it in order to understand it more. I am ready to actually use the software and see some of these processes actually happen. 

 

Chapter 6

Chapter 6 is about mapping what’s nearby. By mapping what’s nearby, you can find out how and event or activity affects an area and features inside of it. There are yet again a million different questions you need to answer in order to determine how you map and analyze your data. To identify what is nearby you can use: straight line distance(Defining an area of influence around a feature, and creating a boundary or selecting features within the distance) , distance or cost over a network(Measuring travel over a fixed infrastructure) , or cost over a surface(Measuring overland travel and calculating how much area is within the travel range). You can use straight line distance by creating a buffer to define a boundary and what is inside it, select features to find features within a given distance, calculate feature-to-feature distance to find and assign distance to locations near a source, or create a distance surface to calculate continuous distance from a source. When measuring distance or cost over a network, GIS identifies all the lines within a network and you can then find features around the area. When calculating cost over a geographic surface, GIS creates a raster layer where the value of each cell is the total travel cost from the nearest source cell. Again, I read all of this information and it feels like a lot but I am excited to see what I can do and learn from using the software next week.