Income data on a block level: how does a newbie do it?

Question

I am a complete newbie at GIS data, and am trying to do the following:

1. Figure out census blocks in Miami-Dade (and several other counties) that have average household incomes > $75,000
2. Get the latitude-longitude boundaries of those blocks
3. Plot the blocks on a map

1 and 2 are the most important. What is the best way to get this data, and then the lat-long boundaries? Quickest, easiest, cheapest are of course the top criteria.

Answer 1

I don't think you can get income data at block level for privacy issues. For blocks, you can only get population and households. As far as I know, the lowest level of geography you can get income data for is block groups. Block groups typically contain between 600 and 3000 people, have an optimal size is ∼1500 people and ∼30 blocks, though in Miami-Dade BGs might be smaller. Block group boundaries follow visible and identifiable features and they tend to be fairly demographically homogenous. Starting in December 2010, five-year period estimates are available for census tracts/block groups from American Community Survey. That data will give you the lat and lon for the centroid of each block group. You might be able to even make the map using the Map View in FactFinder.

Answer 2

Well if you were doing it in ArcGIS then it would probably be easier to do it in the opposite order. There is US Census data freely available.

Boundary files are here: http://www.census.gov/geo/www/cob/

Then you just need to append the data onto the attribute table. If you already have the average household income data with Census Tract IDs attached, it's a simple matter of joining the tables together. A join is done in ArcGIS based on fields, so if you have two Tract ID fields, join based on that (right click in table of contacts and choose join, then join by that field). Then go to the Selection menu, pick "Select by attributes" then write something in the field like

"income" > 75000

And it will select all tracts with those characteristics. Then you can export the data into a new shapefile (right click in the table of contents and choose export, and ensure you export it as a shapefile rather than a layer file, and choose to export the 'currently selected features')

There you have it. :)

Answer 3

Be warned, joining census data to census tigerline shapefiles is a bit more complicated than a simple join. Downloading 2010 or 2000 Census Blocks is simple enough and can be found here:

http://www.census.gov/geo/www/tiger/tgrshp2010/tgrshp2010.html

When you select the file type you want there will be an option to download either the 2010 or 2000 version.

To get income data you will need to get it from the 2000 census because I don't believe income data has been release in the 2010 census yet. 2000 Census data can be found here:

http://www.census.gov/main/www/cen2000.html

You will need to find what summary file contains the information you want. Each summary file is broken out into multiple files containing different attributes so you will need to find which one has the attributes you want. There is also a geographic header file that you will need as well.

In summary you will need to extract the data you want, convert to excel spreadsheets, join the summary file attributes to the geographic header file then join that to the census geography. Make sure you using the correct summation level joining the data.

Reading the technical documentation is immensely helpful.

Good luck, hope this helps.