County Maps Lab
Understand how vector data is designed and stored.
Understand what is in land cover and gazetteer files.
Understand the structure and importance of a shapefile and a Geotiff.
Understand DEM/Grid Manipulation and Formats
Clip a dataset to cover just a region of interest.
Find the difference between two grids
Prepare a final map with cartographic features (legend, scale bar, graticule or labeled grid).
Maps, each with a scale bar, legend, and graticule or labeled grid.
3DEP elevation, clipped to show just the county, with the TIGER file overlaid.
NLCD, clipped to show just the county, with the shapefile TIGER overlaid, for 1992, 2001, 2006, and 2011. Display these so you can easily compare them.
A map showing the parts of the county that changed from 2001 to 2011.
A map showing the 1000 foot drug free school zone around the schools in your neighborhood. Consider the scale at which you should show this data.
What would you have to do show the change in land cover from 1992 to 2011? You do not have to do this, just think about what will make it harder than the 2001 to 2011 comparison.
How well do you think the county masking worked, and what limits the results you can achieve?
Compare the storage (file size) for the Tiger edges file, the NLCD in the Geotiff format that you originally downloaded, and the DEM (all after you decompressed them). What do you think accounts for the differences?
You already have the TIGER Edges file from the last lab. From that File's Metadata you can get the bounding box for the county, which will help you in selecting data. You should err on the side of getting too much data, rather than too little, since you can select a smaller map area in the GIS. For the NLCD you must put a buffer on the region you select because of its conical projection, or you will miss part of the county. The NLCD files are small, and skimping on the area you want is a false economy, unless you want to redo the analysis.
You are likely to need GDAL; this would be a good time to download it.
Get the following data sets for your county, and unzip them. Data organization will be important. You should make a directory for this lab, and subdirectories for each of the data sets. Save the data files for this lab, because we will be using them for the next lab. If you have trouble recognizing what each data set is, you should look in the Metadata.
The 3DEP for your county. You can get either the 1" or 1/3" or 1/9" data (smaller spacing shows more detail but makes for bigger files; your choice will depend on the size of your county, and whether 1/9" data is available), and insure that you get the Geotiff format if at all possible. You might have to get several tiles and merge them. If your county is truly huge, try getting the 3" SRTM data instead, recognizing that it has lower resolution and quality.
NLCD-1992, 2001, 2006, and 2006 (National Land Cover Dataset - Land Cover) for your country. Get the Geotiff format. Insure the program can recognize this data set. Insure your file names include the year. This will be tiled. You will have to go to MLRC to get the 1992 data, where you can get just the area you want, and will not have to merge tiles.
Get a County outline shapefile. There are several options, and you should consider which you want, based on the discussion at the link.
Most operations on a DEM or grid are not saved unless you explicitly do so. The DEM is stored in memory for fast access. In contrast, most changes to vector data happen as soon as you request them, except for filters. If you are concerned about losing data, make copies. The vector data sets are much smaller than the rasters we are using in this lab.
Saving files. Give the files meaningful names, and put them in a directory where you can easily find them.
Data type: you will have NED, and NLCD, and for the NLCD, you must include the year. While we can treat the NLCD like a DEM, it is really a grid with a different interpretation of the data values. You cannot do arithmetic that will make sense on the values.
Reprojected data. You can just call it reprojected, or list the new projection in the name.
Mask/clip to show just the county.
Map gallery for lab. Look at this to understand why we will go through a number of processing steps with the data. This lab will create a large number of data files.
Steps to follow:
Limit maps to just the county area.
Statistics on the NLCD land cover
Difference in the NLCD between two time periods
Use the Raster GIS, Co-occurrence matrix of two grids to get a table showing a summary of how pixels changed. This will let you know if there is basically nothing to see. Most of the time when there appears to be no change, you did the difference between one grid and itself, often because you did not name files carefully.
Option on Raster GIS, Change map which will make a map with two categories, change (1) and no change (0).
Use gazetteer to create a buffer on the map:
last revision 1/23/2017