On 26/11/2009, at 09.47, Morten Kjeldgaard wrote: > Conversely, there isn't much you can do with graphs that can't be done > with areas, and since the "map-drawing" approach has great appeal to > people enjoying beautiful and detailed maps, the pressure for > deprecating the graph-based approach in favour of the map-drawing > approach will be ever increasing.
There is a construction that might "bridge the gap" between areas and graphs. In lack of a better word, I will call it a "multiplex" for now (I am sure there's a better word.) Imagine an area like seen in the attached file (ASCII art). It represents an area that could be an intersection. On the edges of this polygon some "hot-spots" labelled A-H have been defined. The shape of the polygon and the position of "hot-spots" on the edges is arbitrary and can be defined by the user. The nice thing about the multiplex is that lines (ways) can connect to the "hot-spots" from the outside, and the multiplex itself contains information about how the hotspots are connected internally. So for example, if the multiplex in the example represents an intersection, you would connect B->D (left turn from B), B->F (going straigh ahead from B), B -> D (right turn from B). And so on, to make all other possible connections inside the intersection. This would give you an object which would render nicely as an intersection, and there's of course the option of tagging a bunch of auxilliary information such number of traffic_lights, directional signs etc. (This example is for right-lane traffic. In countries with left traffic, you'd do it differently) Cheers, Morten
--C--D-- | | | | ------ ------ | | A E | | B F | | ------ ------ | | | | --G--H--
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