Collaborative mapping is the aggregation of web maps and user-generated content, from a group of individuals or entities, and can take several distinct forms.
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Collaborative Mapping applications vary depending on which feature the collaborative edition takes place: on the map itself (shared surface), or on overlays to the map. A very simple collaborative mapping application would just plot users' locations (Social mapping or geosocial networking) or Wikipedia articles' locations (Placeopedia). Collaborative implies the possibility of edition by several distinct individuals so the term would tend to exclude applications such as wayfaring where the maps are not meant for the general user to modify.
In this kind of application, the map itself is created collaboratively by sharing a common surface. For example WikiMapia adds user-generated place names and descriptions to locations. Collaborative mapping and specifically surface sharing faces the same problems as revision control, namely concurrent access issues and versioning. In addition to these problems, collaborative maps must deal with the difficult issue of cluttering, due to the geometric constraints inherent in the media. One approach to this problem is using overlays.
Overlays group together items on a map, allowing the user of the map to toggle the overlay's visibility and thus all items contained in the overlay. The application uses map tiles from a third-party (for example one of the mapping APIs) and adds its own collaboratively-edited overlays to them, sometimes in a Wiki fashion. If each user's revisions are contained in an overlay, the issue of revision control and cluttering can be mitigated.
According to Edward Mac Gillavry there is a dichotomy between corporate projects and user-driven projects. With corporate initiatives generally using a one-way information flow from the service provider to the subscriber and user driven projects generally being characterized by a two way information flow.[1]
Several big internet companies launched mapping applications with collaborative features, most importantly Google Maps with the Google Map Maker feature. Although Google allows flexible mash up style use of their raster map images, the MapMaker system presents a one-way flow at the level of raw map data, from the community to Google (with the exception of some areas where special provision of shapefiles have been granted for humanitarian reasons). Contrast this with the similar non-corporate collaborative mapping system, OpenStreetMap, which allows all raw map data to be downloaded freely and openly via API requests or full "planet" download.