Pamela Fox wrote a post on Google Maps Blog that details how to create a map from a Google Spreadsheet that contains geographical information.
First you need to build a spreadsheet that has a header and a list of locations described by title, latitude, longitude. There's a nice batch geocoder that uses Google Maps API and can help you build your spreadsheet: copy the generated text in a text file and import it in Google Spreadsheets.
Once you have the spreadsheet, you need to create the connection with Google Maps. There are three ways to do that:
- The simple way. This page requires to modify the URL and add the key parameter from the spreadsheet. That's all: no customization, the spreadsheet must have fixed column names, no embedding option.
- Almost as simple. This wizard lets you customize the map and embed it in your site.
- The hard way. Use Google Maps API and Google Spreadsheets API to build your own application.