The v parameter within the http://maps.google.com/maps?file=api&v=2 URL refers to the version number of the Google Maps API to use. Most users of the API will want to use the current “Version 2” API by passing the v=2 parameter within that URL. You may instead obtain the latest release (including the latest features) by passing v=2.x instead. However, be aware that the latest release may not be as reliable as the v=2 release. We update the Google Maps API often (sometimes every week), at which point features within the v=2.x release are migrated into the v=2 release unless problems are discovered.