Bryan Week 3

Chapter 4

• Mapping the density of features helps you see the patterns of where certain things are concentrated
• Density shows you where the highest concentration of features is in your map. Good for looking at patterns rather than individual features.
  • This is useful for analyzing things such as census population or number of burglaries within an area.
• Can be used both for features (locations) and feature values (eg. Number of employees at a business).
  • This makes density maps more versatile and able to be used by a much wider audience for a more varied amount of analysis needs.
• You can use either dot mapping or cell layers to form a density map.
  • Density surface (cells) shows more information, but requires more effort to make.
• Density surface can be used for individual locations or linear features (roads, rivers, etc.)
• You should map by defined area if you already have the data you need summarized, or if you want to compare areas with defined borders. A density surface map is needed if you want to see the concentration of points or line features.
• There are also two different ways to display density maps; you can choose to use either gradual colors or a contoured map.
• Contour maps are good for showing the rate of change across a surface of the map, with closer lines indicating a faster rate of change.
• Gradual color maps are more cell-like with layers of color to display the data. For example, you can use a light color over a dark background to shower higher density, or vice versa. 

 

Chapter 5

• People map a specific area to monitor what’s going on inside of it, which can be used to compare what’s going on inside several different areas
  • This helps them know whether or not they might need to take action regarding the problem they are trying to monitor / analyze.
  • This can be used for policy changes, deciding specific penalties, etc.

• For your data, you need to consider how many areas you have, and what types of features are within the area.
• With GIS, you can find what’s within just one area, or several.
• Discrete features are unique, identifiable features that can be listed, counted, or summarized. They can be things like student addresses, crimes, or linear features such as rivers and pipelines.
• Continuous features are seamless geographic phenomena, such as the soil types within an area, or the number of inches of rain per year. 
• Continuous values are numeric values that vary continuously across a surface, such as temperature or elevation. 
• The GIS can help you see whether or not an individual feature is inside of an area. 
• There are three ways to find what’s inside the map
  • Drawing areas and features for a visual approach. This is done by collecting the data set containing the boundary areas, and a dataset containing the features.
  • Select the features inside of an area to get a list or summary of the features within an area.
  • The GIS combines multiple layers of maps to overlay the areas and features. This is useful for finding which features are in each of several areas or finding out how much of something is in one or more areas.

 

Chapter 6

• Mapping what is nearby allows you to see what is within a set distance or travel range of a specific feature. This helps with monitoring events within an area, or finding the features affected by a particular activity.
• Traveling range is measured using distance, time, or cost. Finding out what is within the traveling range of a feature allows you to define the area defined by a facility.
• To find what’s nearby, you can measure straight-line distance, measure distance or cost over a network, or measure cost over a surface
• Distance does not always equal nearness. You can also measure using cost, of which time, effort, and money are the most common. 
• You have the option of calculating based on the assumption that the earth is a flat surface (planar method), or you can account for the curvature of the earth (geodesic method).
  • The planar method is useful if the area of interest is relatively small, such as a city, county, or state.
  • Geodesic method is good for when your area of interest is much larger, encompassing an area such as a region, continent, or the entire earth.
• Using a straight-line distance to find what is nearby is useful for when you are trying to create a boundary or selecting features within an area. This method involves specifying the source feature, and then having the GIS find the area or surrounding features within the distance. 
• You can also use the GIS to find  which segments of the network are within the distance or cost of the source locations.
• This can also be done using the associated travel costs.
  • Use straight-line distance if you’re defining an area of influence or want a quick estimate of travel range.
  •  Use cost or distance over a network if you’re measuring travel over a fixed infrastructure to or from a source.
  •  Use cost over a surface if you’re measuring overland travel.