2012/1/14 Russ Nelson <nel...@crynwr.com>: > Lester Caine writes: > > yet there seems to be no way to create secondary databases of > > information which can be used in parallel but separately hosted. > > Yes, we need *more* OpenStreetMaps from which you can fetch different > types of information. For example, any data which is externally > maintained and updated really *shouldn't* be imported into OSM.
If you really want to connect the data you will have to have it in one database. Layers are only good for stuff that is not connected/linked, i.e. that is independent from each other (rarely the case for features like the ones we are talking about here, as existence of the roman road had an influence on the further development of the road grid). E.g. if you have a building of which the basement is roman and the upper parts are medieval (we can asume for this example that they both occupy the exactly same area), and you realign the upper parts (say you slightly move 2 corners) you will also want the lower one to follow this modification. The both are linked and for consistency a refinement of one will (in many cases) require also the other to be modified. We would need to have a way to link 2 datasets like: this line in dataset A is the same as this line in dataset B (or this line in A is parallel to this line in B). If you continue to think this and think about the complexity of the real world (there is not only a few lines but many of them, and they are not only the same or parallel but also orthogonal, or in the middle/center, or ...) you will see that you either keep them in one dataset or you will loose all these relations. Layers work well if both are only loosely linked (say you have temperature measurements in a grid and overlay them with OSM data for visualization). cheers, Martin _______________________________________________ talk mailing list talk@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk