Google is looking to increase the range and variety of information with a geographical element that it offers, and hopes its users will play a big part in the expansion.

The company's two main geo-linked tools, Google Earth and Google Maps, are already host to an expanding universe of geographically-tagged content. Some of it comes from Google, like the recently added map layers that display geographically relevant Wikipedia articles or photos from the Panoramio Web site. Users can make their own data sets using Google Earth and publish the results as a KML (keyhole markup language) file, which other users can download and add to their copy of Google Earth.

"We want to expand and add more regional information to the geo Web layer," said Peter Birch, product manager of Google Earth. He was speaking after a news conference on Monday at which Google launched a PC-Web based public transport route planner for Japan.

Birch hopes the increasing usefulness of geo-tagged information will push users to add their own to further enrich the scope of data available. And he offers evidence to suggest that might happen.

Panoramio, the Spanish photo site that specializes in photos of landmarks taken with cameras that can embed GPS data has seen membership rocket from around 100,000 in January, when Google added the layer, to more than 1 million users now, he said.

"Take a look at this," he said, spinning a laptop computer around. A quick search of Google brought up a dataset for an overlay showing railway stations in Tokyo. A couple of clicks later and they were overlayed on a satellite image. A couple more clicks brought up Wikipedia articles on Tokyo landmarks and photos from across the city from Panoramio, all overlayed on the image.

"If you're visiting Tokyo you want to be able to look at an area and see what's around it," he said while demonstrating how this small handful of layers added not just images and information on landmarks but also made it easy to figure out nearby railway stations.

While KML datasets and GPS data embedded in photos make it easy to integrate the content with Google Earth of Maps, there's no standard was to add geo-tagging to a Web page that would enable a news story to be tagged with where the event happened, or allow a company to add a locator for its offices.

There exists a Geo RSS protocol that enables the embedding of geo-data in RSS feeds and Birch said he expects the same to happen for Web sites as geography-related applications become more common on the Web.