Google is taking GPS makers head on with Google Maps Navigation, a turn-by-turn feature that runs on new versions of its Android cellphones.

The company unveiled the new feature, which is downloadable for phones running its Android 2.0 operating system, on Wednesday. So far, the only phone that runs the new operating system is the Motorola Droid, which will be launched next week by U.S. cellphone carrier Verizon.

The new Navigation feature improves upon existing GPS devices in a number of ways, Google said:

• Because it runs on an internet-connected cellphone, the feature always has the most up-to-date maps and information, unlike traditional GPS devices which must be removed from the car and attached to a computer to get their refresh.
• It uses the same search functionality as the Google search engine, so a user can type in a business name or type rather than a specific address. Navigation also has voice search.
• As with its existing Google Maps feature for smartphones, Navigation displays live traffic data, with roads coloured either red, yellow or green depending on how congested they are.
• Like Google Maps and Earth, it has layers — including satellite imagery
• It automatically switches to Google Street View when the user nears his or her destination.

Google's phone-based GPS system, which will go toe-to-toe with market leaders Garmin and TomTom, also has a number of disadvantages.

The Android feature will not work where users can't get cellphone reception. It would also be prohibitively expensive to use outside of the cellphone owner's home country because of high data roaming charges.