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.