Elly Waterman wrote:
In the Netherlands, most GIS data are owned by publicly funded organisations, but cannot be used freely. To the contrary these data a very expensive.
This is the case in most of Europe. The issue is discussed on the EGIP mailing list (European Geographic Information Policy), http://www.ec-gis.org/egip/
The aforementioned GRASS and other free mapping software are discussed on the FreeGIS mailing list, http://intevation.de/mailman/listinfo/freegis-list
Both lists have archives available online.
Most GIS systems are organized as "layers", such as rivers, roads, city names, county borders, elevation, vegetation types, etc. To compile a map for a specific purpose, you select some of the layers, a particular area, scale (zoom), and projection (transformation of coordinates). The more layers we can make available, the better. But a wiki-like project could be useful even if it only produces a few such layers, for example a list of city names and their coordinates. This can easily be edited in text using today's wiki technology. In Wikipedia's case, each name (of cities, counties or rivers) can also be tied to the disambiguated name of a Wikipedia article, so clickable maps can be compiled.