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The OpenStreetMap (OSM) project is well on its way to producing a free, user-editable street-level vector map of the world. OpenAerialMap (OAM) is similar in scope, committed to building a free, bird's-eye photographic map of the world. But it faces a unique set of challenges.
For covered areas, the experience is similar to that of proprietary tiled geodata services like Google Maps, MapQuest, and Yahoo! Maps. As you zoom in, the server replaces tiles with higher-resolution shots when available, and falls back to enlarging smaller tile images when necessary. The chief difference is that -- as a free service -- the project cannot afford to purchase aerial photos from the commercial mapping services.
Unlike OSM's reliance on user-collected GPS data, though, OAM's main sources of imagery are existing, reusable aerial photo sets -- and there are plenty to choose from. The National Agricultural Imagery Program (NAIP), for example, collects aerial photographs of the United States in order to study the agricultural growing season. As a taxpayer-funded US goverment program, the collected data is in the public domain.
Numerous other agencies and governments at the state and local level gather similar aerial photographic data that can be collected, processed, and loaded into the OAM database. OAM project participants can load the data, and OAM can also import data directly from other Web Map Service (WMS) providers.
Project founder Christopher Schmidt and others are currently leading the data import, but as Schmidt told the project's mailing list, he hopes that eventually the organizations collecting the original data will feel comfortable contributing it to the project without a middleman. "I think that the best thing in the world for everyone would be if OAM could be seen as a place where governments and other organizations can share their imagery with the world without the need to worry about hosting or setting up a Web service. They simply create data records, upload the imagery, and are done."
Schmidt launched the project last fall, when he decided that OSM lacked the underpinnings to do serious geographic information system (GIS) work. That means registration of map data, overlay of multiple data sources, and potentially more complex analysis and transformations.
Whether OAM will ever implement complex GIS functions remains to be seen; right now the project is focusing solely on collecting surface imagery of the Earth. But you can already use OAM data as a data source in other GIS applications, such as NASA's World Wind, or any WMS client.