Downloading Census Data (and getting it into ArcGIS)

In this exercise we’ll download data from the US Census Bureau and join it to a shapefile.  We’ll also explore raster population data sets.  You’ve done join’s before but never with “real” data.  This exercise is an introduction to the census website.

1. American Factfinder
2. On the left side click data sets > decennial census
3. Choose Census 2000 Summary File 3.
4. Click Detailed Tables
5. Choose “geo within geo”
6. Under the “Show me all” drop down list choose tracts
7. Choose State from the “within” list.
8. Select a state
9. Select “all census tracts” and then click the “add” button.
10. Click the “by subject” tab and select a subject of interest.  Click search and then “add” the table to the list of data you want to download by clicking the add button.  Be sure to include total population.
11. click show result.  The result is a not very readable table that is probably spread over hundreds of pages.  We want to download the table so that we can map it.
12. click download from the blue bar near the top of the page.
13. Select Microsoft excel under “database compatible.”  Keep the “include descriptive data elements” box checked (it should be checked by default).  These descriptive data elements describe the contents of each column.  Without the descriptive elements the columns have names like “P155A001″.
14. You have to edit the file you downloaded.  To work in ArcGIS an excel file must have “header”, a single row that contains the names of each column.  You can rename the columns based on the descriptive text in the second row (and then delete the second row) or you can retain the original codes.  I do this by copying the first two rows of the file (by typing ctrl-c).  I then open a new excel workbook and choose “paste special” from the drop down list under the word “paste” on the “home” tab.  In the paste special dialog I check the “transpose” box, the result should be list where one column contains a description and the other column contains the code associated with each variable you downloaded.

Now we need to download a map of the census tracts for the state you selected.  This is done through a seperate census website.

1. Go to the 2009 Tiger/line files main page
2. Select your state from the list on the right side of the page.
3. Download the census tracts for the 2000 census – its confusing, I know.  The website with the census 2009 boundary files includes a ”census tract (census 2000)” data set.  This file contains the boundaries of the census tracts used to report the data collected during the 2000.
4. Open the downloaded files in ArcGIS.
5. Join the excel table to the shapefile.  The unique IDs that you’ll use for joining are “CTIDFP00″ (in the shapefile) and “GEO_ID2″ in the Excel File.

Now we’ll download a raster population data set for North America.

1. Go to CIESIN SEDAC Gridded Population of the World website.
2. In the upper right “switch region” to north america.
3. Select GPWV3 “population grid”
4. Choose the Grid format and the year 2000.
5. Extract the zip file and add it to your map.

Next week we’ll learn more about working with this type of file.  and integrating raster and vector data an analysis.