That file caches the locations displayed by your maps and saves the latitude and longitude associated with any addresses you have mapped.
It is used to speed up the page as well as to prevent your page from running into daily limits google imposes on using their geolocation services.
It is supposed to be updated automatically, but you can add it to your gitignore file without any problems. It will be updated automatically if it ever gets cleared out the next time the map is displayed.