title: Determine census tract of US address
body: <p>I have a list of about 20k addresses in the US, and I would like to determine each one's census tract. I found a tool online that does this <a href="http://www.ffiec.gov/geocode/default.aspx" rel="nofollow">here</a>, but making 20,000 requests and screenscraping the output seems like the wrong way to do.</p>
  
  <p>One idea I had was to use some open source library like <a href="http://virtuoso.rubyforge.org/rgeo-shapefile/" rel="nofollow">this</a> to search the shapefiles provided <a href="http://www.census.gov/geo/www/cob/tr2000.html" rel="nofollow">here</a>. However, it seems like someone should have written a utility to do something like</p>
  
  <p>Geocoder.census_tract_of_address("200 N State Chicago IL 60601")</p>
  
  <p>Does anyone know of such a thing? How best should I attack this problem?</p>