Geocoding Addresses

A common need: given a physical (mailing) address, find the geographical coordinates in order to display that location on a map.  This is called "geocoding."

Geocoding with Web applications

• some will resolve street addresses in the U.S. and most international city names
• Free Geocoding Services (dan goldberg at USC)
  • uses TIGER, so it's US-only
  • free for non-commercial purposes
  • also has some more accurate data where they have coverage (e.g., parcels in Los Angeles)
• batchgeocode.com
  • Supports USA, and most countries in western Europe.
  • It says "this site uses Yahoo's Geocoding API which is based on NAVTEQ and Tele Atlas street data", hence it can give more accurate results than a TIGER-based geocoder.
  • It's rather slow, but free.
• Eagle (Geocode.com / Tele Atlas)
  • the web page lets you try their engine, one address at a time
  • commercial service, US Only, minimum $50 for 1000 addresses
• Geocoding Service - TravelGIS.com
  • also provide free single-address lookup, and directs you to NACGEO.com for commercial geocoding of many addresses
• iBegin Geocoder is yet another commercial site (up to 100/day free) with US/Canada coverage, although when i tested, it could not resolve a US address.
• at one point it was possible to get the geographical coordinates back from MapBlast!
  • the lat-lon was embedded as text in the response, so it could be parsed out
  • it seems that during 2001 they removed the lat-lon from the result for international addresses, and as of late 2002, it was removed from US addresses as well
• Mapquest results do not contain lat-lon, but they have a good page describing geocoding

Open Apps/Libraries

• geocoder.us is a (conditionally) free web server
  • uses TIGER, so it's US-only
  • free for non-commercial purposes, and the engine is open-source so anyone can make their own service
• PAGC-Postal Address Geo-Coder
  • a C library, on sourceforge
  • takes as data any shapefile with sufficient attributes, such as is available for USA (from TIGER) and Canada

USA Data

• the TIGER dataset is the natural public-domain database to use, if creating your own geocoder
• alternately, it's fairly easy to geocode roughly by zip code
  • all that is needed is a list of geographical locations for zip codes.
  • such a list is included with ArcView and other GIS programs
  • nnoncommercial sources are typically out of date (e.g. 1990), however the SmileConnection site offers a free database, updated monthly,  with lat-lon point per zipcode
  • there are many commercial sources for up-to-date zipcode data, e.g. Zip Code USA
• the US Gazetteer can be used to look up city name in the US
  • derived from the Census GICS
  • uses Place and Zipcode files
• GNIS: the USGS Geographic Names Information System
  • contains information for almost 2 million physical and cultural geographic features in the United States and its territories
  • GNIS - Fact Sheet 127-95 has more information about the dataset

International Data

• NGA GEOnet Names Server
  • PUBLIC NGA GNS Names Files of Selected Countries is a set of text files, one per country outside the USA, which contain the coordinates of every named place
• Latitude & Longitude - Look Up has some information about international cities
• GTGN - Getty Thesaurus of Geographic Names
  • includes lat-lon for many of its geographic place names
• Canada
  • Querying Canadian Geographical Names is awkward to use, but does provide coordinates
• WhereIS can resolve many Australian addresses that the other map engines can't, but it doesn't provide coordinates
• Guide to Australia - Search for Latitude & Longitude of Towns in Australia

Geocoding from Internet Addresses

• MaxMind GeoIP
  • a commercial (but inexpensive) database which maps IP address to country, region, or city
  • uses given are to "analyze web logs to locate clients, geo-target banner ads, detect credit card fraud, auto-select country on forms, prevent password sharing and abuse of service, and display native language and currency."
  • $50 for mapping to Country, $100 for Country/US State, $300 for City
  • they claim 95% accuracy for the mapping to Country
• IP2Location
  • another commercial service
  • $50 for mapping to Country, $200 for Country and ISP or City, $500 for Lat-lon
• hostip.info
  • Community-based project to geolocate IP addresses, making the database freely available.
• the GeoURL project (GeoURL ICBM Address Server)
  • an experimental mapping of URLs to coordinates which indicate the location of the thing which the URL describes, rather than the location of the web server
  • this allows you to find URLs by their proximity to a given location
• javainetlocator
  • "The fastest, most accurate IP geolocation system in the universe. Built by professionals. Freely distributed."
  • provide instructions on how to build your own database
• IP:Country
  • a Perl module which aims to provide country lookup - less ambitious (and more reliable) than attempting to resolve to geographic location