- What geometry level (block, block group, or tract) would be best to use, and why? Include a table with the number of polygons at each level for your county, and the mean and median sizes for each in both square kilometers and square miles. For the 2000 Census, you could get data for each geometry. For the 2010 census this is no longer true, and we can only get the tracts. Why do you think the Census Bureau no longer distributes detailed data for the blocks? You might consider the average population for polygon at the different levels, and privacy issues.
- What are the advantages and disadvantages of the different ways to display the map data (color coding and scaled symbols)?
- Which is better, population numbers or population density, for a map of the county? Why?
- What names did you pick for two of the fields that were not converted? How hard or easy was this, both in terms of the procedure, and in finding a "good" name?
Data Acquisition
| Download, Do early | Data Layer | File name and location on your hard drive |
| Yes (should be simple) | Download Tiger Census Blocks shapefile | |
| Subset Blocks shapefile to just your county (filter with county FIPS codes) and save | ||
| Yes (should be simple) | Download Tiger Census Block groups shapefile | |
| Subset Block groups shapefile to just your county and save | ||
| Yes (should be simple) | Download Tiger Census Tracts shapefile | |
| Subset tracts shapefile to just your county and save | ||
| Yes (big but simple) | Download National coverage Census Bureau SF1 shapefile by tracts (it has a metadata file with it) | |
| Subset SF1 shapefile to just your county (filter with county and state FIPS codes, which are the first 5 characters of the GEOID field, so use GEOID='24003*') and save. Because of the size of this file, the subset is critical (or you will sit around a lot). | ||
| Rename fields in subset SF1 | ||
| Yes; will be complicated | Download American Community Survey Data for your county, by tracts | |
| Modify CSV file from American Community survey (rename a few fields, and delete the rest) | ||
| Import American Community survey as DBF file. If you have a
coastal region, there are often tracts with 0 population. These
will skew your color coding by field, and it will probably improve your
map if you filter them out and perhaps save the shapefile without them. Add leading zeros to repair Zip or FIPS codes. |
Data analysis:
- Open a map.
New DEM. With a
reflectance map, this provides a very nice background, but you can use any
base map you want. The TIGER edges on top might provide additional
context. You will be trying to understand where in the county things are
happening, and a good base map really helps.
-
Open
shapefile map that covers just the region of the
shapefile.
- Link/join the demographic data to the
shapefile with region outlines.
You must correctly match the geometry with the correct demographics (you
cannot match block groups with tracts, for instance) for the ACS data.
- In the census demographic data, the linking field is GEO_ID2, unless you renamed it.
- Plot maps of parameters from the
"Plot"
button menu on the database
table display
window,
- Color code by DB field
- Proportional symbols plotting
- If there are tracts along the coast with 0 population, you should filter then out. Otherwise they can cause a lot of color to be wasted, since the lowest actual value should be 0 rather than the artificial 0.
- Insure that you consider opacity for the display.
- Computations you want
- Compute area.
- Convert area to square miles:
- Edit, Field arithmetic, Copy numeric field to make a new field. You could just operate on the original field, but you must be careful that the size and precision of the field will work. In this case, square kilometers and square miles are close enough that it should work. If you were converting square meters to square kilometers, you need a much shorter field, but probably many more decimal places.
- Edit, Field arithmetic, Multiply field by constant (Google the conversion factor)
- Compute ratio (e.g. population density, or male/female ratio): Edit button, Field arithmetic, Quotient 2 Fields (ratio)
- Get the mean and median of the area field with Stats, Moments, or Double clicking on field name and picking Field stats.
- Double click on the area field header, and get Field statistics (min, max, mean, etc.) Make a table with this information
- Adjust the color in the underlying map to de-emphasize the background and let this data dominate, but the background helps the viewer locate the points of interest.
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Last revision 9/13/2018