Geocoding is the process of assigning geographic coordinates to locations designated by some other parameter, like name or address. Google Earth Plus lets you geocode up to 100 US addresses in spreadsheet form, assigning them a location. But there are a number of tools that can do this for free, and in some cases allows you to process more than 100 addresses at a time.
BatchGeocode (website; free, but donations accepted)
This site will take a tab or bar-delimited spreadsheet file with addresses, geocode the address, and then creates a product spreadsheet file with the latitude and longitude appended to every address line. An Excel template is offered to help with the tab-delimited format (opens in the free OpenOffice spreadsheet as well). You can copy and paste the product spreadsheet data back into a spreadsheet program, and then export it in CSV format for use in csv2kml; this gives you additional flexibility in what information gets included in the KML file. But BatchGeocode also offers the option of directly creating a KML file on the website from the address and position location; more convenient, but you have less flexibility in how the spreadsheet information gets included in the KML file. BatchGeocode uses the Yahoo geocoding engine, and links your IP address to your request, so you can geocode a maximum of “only” 5000 addresses a day.
GPS Visualizer (free, donations requested)GPS Visualizer will take a spreadsheet address file in tab or comma-delimited form, geocode it, and then give you output either in a text spreadsheet format or in GPX format (which Google Earth can open). The options for including information beyond the address and a basic description seem limited. GPS Visualizer also has an unstated limit on how many addresses you can convert, stating that if they find your IP address geocoding too many addresses, it will be blocked.
Juice Geocoder (free Excel spreadsheet; scroll down to the Tools section)
If you have Microsoft Excel with VBA enabled, you can use this spreadsheet with macros to geocode a set of addresses, and convert it to a KML file. You’ll have to sign up for either the free Yahoo or geocoder.us services to use this spreadsheet. But again, there are limitations on how you can incorporate info in the KML file.
Overall, I’d say that BatchGeocode is the best of the bunch. But keep in mind that none of these will necessarily plot the address in the exact location. For my house, most of the geocoders were off by about 125-150 feet, but the Juice Geocoder (using Yahoo) was off by close to 700 feet.
If you’re really motivated, you could always try using or modifying one of the following free open source geocoding solutions to meet your needs. Not me, thanks.
ajmGeoCode PE (free limited edition)
Comes in a compiled version that limits you to 50 addresses with registration, but the source code is available and open.
Winner of the 2002 Google programming contest. But it uses US Census TIGER data for geocoding, and that data source is slightly inaccurate in many areas of the country.
Also uses the TIGER data.
Portfolio Encoder Open Source
I’m not aware of any comparable geocoding services for Google Earth for any countries other than the US; if you know of any, please let me know.