For my examples, I’d suggest a look at the GPS games Waymarking [http://www.waymarking.com] and Geocaching [http://www.geocaching.com]. Both are based on community construction of a shared data space layered over real space, and differ in whether the ‘mark’ is purely virtual or involves placing a physical object. Other than being a similar design problem, it’s also interesting to note that both have developed much the same layered delegation of authority and responsibilities to the user community that also appeared years ago in the form of mods/sysops in settings like BBS’, Usenet, The Well and online services. That’s a form of layering that’s probably as important as separation of technical concerns.

Or within a school or community, allow each group to maintain their own data source: soccer team game locations, community gardening centers, interest groups, clubs, etc. and then build a community map from these various data sources.