The downloadable Google Earth 4.0 runs on PCs, Macs and Linux-based machines and is available in localized versions in French, Italian, German and Spanish, according to Michael Jones, chief technology officer of Google Earth. Jones, speaking here at Google Geo Developer Day, said the improvements will eventually show up in the Web-based Google Maps site.

Developers can use Google's SketchUp 3D modeling software to make the images as lifelike as possible, such as adding texture to buildings. Users can also overlay different data on top of the same view. In a product demonstration, Jones showed a 3D view of San Francisco from 2005, and with a click, showed the same view of San Francisco in the 1940s.

"Developers can place images on top of (the map) that span the whole Earth," Jones said, half-jokingly calling it a "time travel" application. "I think people will use it to share ancient maps (and share) information about possible future developments."

Mark Limber, product manager for Google's SketchUp modeling software, demonstrated how to create a 3D building and insert it into a Google Earth map. Realtors can use SketchUp to build models of homes and put them into maps to show prospective buyers, he said. A repository of links to geographic- and nongeographic-referenced objects that can be used is located here.

Jones also showed off the Google Earth Community, which he described as "participatory mapping," in which individuals can add personal placemarks to information on the map.

More than 30,000 developers around world are using the Google Earth application programming interface, and there have been 100 million downloads of Google Earth, said John Hanke, Google Earth and Maps product director.

Google representatives also demonstrated how people can easily overlay geographic data on top of a Google map without hosting a map on a Web site to create a map "mashup." Google is adding geographic-coding support to Google maps so developers can easily get the coordinates for an street address.

The company also introduced Google Maps for Enterprise, which can be used by companies internally and includes service and support. Pricing starts at about $10,000 per year.

Greg Sterling of Sterling Market Intelligence said he was impressed with the improvements in resolution and coverage. "Google is trying to make all these tools more accessible to ordinary people and get them engaged in content," he said. "In addition, the idea of a geobrowser is fascinating, as is the eventual merger of gaming and mapping."