Tuesday, August 12, 2014

Downloading and Extracting US Census Bureau TIGER/Line Shapefiles

The United States Census Bureau (census.gov) site is a great resource for free spatial data such as state, county, census tract, etc. boundary files. These files can be used as is or used as a building block for creating custom sales territories. They can be loaded into SQL Server for use in spatial queries or for displaying boundaries on a map in an SSRS report. They can also be used to build map tiles for use with the Bing Maps API. This post, however, is focused on downloading and extracting these files.

These TIGER (Topologically Integrated Geographic Encoding and Referencing)/Line Shapefiles are available in many vintages, including definitions from the 1990, 2000 and 2010 censuses, with annual updates through 2013 (2014 should be available soon). The Census Bureau site provides several ways to access and download these files, but the easiest way is to use their FTP site (ftp://ftp2.census.gov/).

You can use an FTP client or, as shown here, you can simply use Windows Explorer.

Start by opening Windows Explorer and pasting ftp://ftp2.census.gov/ directly into the address bar. 

Navigate to the geo/tiger/. From this folder you will see the different vintages of TIGER files available. To illustrate the next step, lets say we're interested in the 2013 Census Tract boundaries.

Navigate to the TIGER2013/TRACT folder. In the right hand window (i.e. file list), you'll see a list of compressed (.zip) files with names based on the State FIPS Code, which is a two character numeric code assigned to each state, the District of Columbia and outlying areas of the U.S. (Puerto Rico, Guam, etc.).

Select the ZIP files you're interested in. I'm only interested in the U.S. states and DC, so I'm selecting files tl_2013_01.zip (AL) through tl_2013_56.zip (WY).

Right-click one of the selected files and select Copy from the popup menu.

Navigate to a folder on your local network, right-click the folder and select Paste. This may take a few minutes. I'll wait.

Now that you have the files on your local network, we need to extract (i.e. unzip) them. Unfortunately Windows Explorer falls short when needing to unzip multiple files. If you already have WinZIP or WINRAR installed, you could use either of those to unzip multiple files. I don't, so I'm going to use the following PowerShell script that I found on Steve Schofield's Blog

function UnZipMe($zipfilename,$destination) 
    $shellApplication = new-object -com shell.application 
    $zipPackage = $shellApplication.NameSpace($zipfilename) 
    $destinationFolder = $shellApplication.NameSpace($destination) 

    # CopyHere vOptions Flag # 4 - Do not display a progress dialog box. 
    # 16 - Respond with "Yes to All" for any dialog box that is displayed. 


# replace the following with the folder that contains your zipped files
$a = gci -Path C:\Data\USCBCensusTracts2013 -Filter *.zip 

foreach($file in $a) 
    Write-Host "Processing - $file" 
    UnZipMe –zipfilename $file.FullName -destination $file.DirectoryName 

Once this script finishes running, you will have all of your shapefiles ready to work with.