geocoder.us: a free US geocoder

geocoder.us

find the latitude & longitude of any US address - for free


What is geocoder.us?

Geocoding is the process of estimating a latitude and longitude for a given location. Geocoder.us is a public service providing free geocoding of addresses and intersections in the United States. The geocoding service relies on Geo::Coder::US, a Perl module available for download from the CPAN.

How does it work?

The US Census Bureau provides location data for nearly every street and highway in the US in the form of the TIGER/Line data set, which runs to over 24 gigabytes uncompressed. Geo::Coder::US condenses the 2004 TIGER/Line data set down to a 750 megabyte BerkeleyDB database. A given address or intersection is parsed into its components, and the matching address range is searched for in the database. The address is then interpolated between the endpoints of the matching address range to estimate its latitude and longitude. For urban addresses, the coordinates given by Geo::Coder::US can be within 10 or 15 meters of the actual location -- which is well within the range of typical GPS accuracy! Other times the coordinates can be off, so use your own judgement when using the data!

Datum and Projection

From the Tiger Metadata "NAD83 is the coordinate datum used for the 48 contiguous states, the District of Columbia, Alaska, Puerto Rico, and the Virgin Islands of the United States. Regional datums are used for Hawaii and the Pacific Island Areas."

And

"The TIGER/Line data are not in a mapping projection even though most of the features were scanned directly from source maps (usually USGS 1:100,000-scale topographic quads) that were in a projection."

Read the metadata yourself to get a better understanding of what this means for your applications, and to get a feel for the magnitude of the task that the Census did (rah, rah, go census!).

Is it really free?

You bet it is! Commercial US geocoding services can charge up to $1 per lookup, but the TIGER/Line data on which their geocoders (and ours) are based is in the public domain. The Geo::Coder::US suite is made available free for download under either the GPL v2 or the Perl Artistic License. All data from the free services on the geocoder.us website are provided under a NonCommercial-ShareAlike license, which means you can use anything you get from us for any non-commercial purpose, so long as you give us proper credit and extend the same courtesy to others.

Where do the maps come from?

All of the maps you see on this website are generated by the US Census Bureau's TIGER Mapsurfer, and are in the public domain. They are based on the 1998 TIGER/Line data set, so they may be a little out of date. You can find how to include their maps on your own website from the Census Bureau's TIGER Mapping Service instruction page. The geocoding results are generated using the most recent (or at least close) Tiger data set.

The geocoder can't find my address!

Well, the TIGER/Line data set is notoriously incomplete, but there may be bugs in Geo::Coder::US that prevent it from finding particular addresses or intersections. However, we continually try to improve the quality of our service.

Please send an e-mail to missing@geocoder.us if our geocoder can't find an address that you're sure exists, so that we can refine and improve our code.

How can I make my own geocoder?

You can download the code and the latest TIGER/Line data, and build your own Geo::Coder::US service or application for whatever purpose you like.