The tracking feature, called Latitude, will appear on compatible mobile devices in a new version of Google Maps, version 3.0.0. It can also be added as a gadget on iGoogle, the company's personalizable home page service.
To begin sharing your location, you must either sign up for the Latitude service or accept an invitation to view the location of someone already using it.
Latitude's help pages describe the fine-grained control the service allows over who sees what, and when. For each friend with whom you choose to share information, you can give your precise location, the name of the city only, or no information at all.