OpenStreetMap
I didn't care before if mappers used part of a road as part of a landuse or combined it with something else. During the process of remapping non complient ways, I got a opinion now. DONT use a way for more then one map feature. Trying to untangle river banks from residential landuse which is also part of something else what a freaking mess.
Discussion
Comment from asciipip on 26 May 2012 at 16:57
I’ve dealt a lot with shared nodes in a variety of situations, both created by me and others. I’m not enamored of the practice of sharing nodes between roads and areas, but I prefer if adjacent area features share nodes. That reflects the reality that they abut each other and makes adjustments (if the river shifts course, or just if you’re improving the accuracy of the ways) easier.
One of the two alternatives is using adjacent nodes, which makes adjustments a pain, can make targetting the right node problematic if they’re really close, and doesn’t reflect the situation on the ground.
The other alternative is building multipolygons out of shared ways. I used to do area features this way, but found that the tools we have don’t always deal well with this, and (subjectively speaking) they seemed to be broken by other mappers more often. These days, I try to make area features with continuous, closed outer ways, even if I need to use a multipolygon to add inner ways. When I need multiple outer ways (because there are more than 2000 nodes along the perimeter, usually), I try to break it into pieces in such a way that the line between the endpoints of each piece remains entirely in the interior of the feature, although it’s not always possible to do that.
Comment from robert on 26 May 2012 at 19:14
Agreed with asciiphil.
Node sharing is very good for conjoined areas. The tools aren’t always great at dealing with them though.
Comment from Pgd81 on 27 May 2012 at 13:07
I’m still pretty new, but yep that’s the opinion I’ve arrived at too. Ways should share nodes with ways, areas should share nodes with areas. But small rivers & streams are an exception if they form a border of e.g. an administrative area or property boundary.
Comment from Sam Wilson on 28 May 2012 at 00:52
I used to do far more shared nodes than I do now, because I’ve started just mapping exactly “what’s on the ground”.
A stream, for instance, is a way down the centreline of the stream, and one area (often) on either side, following the riverbank.
Two areas will usually have some sort of boundary, which I map as a way set between the two areas.
The only time I share nodes is when the boundary between them actually has no width (e.g. is a imaginary line between two survey points or something).
Just makes it easier to edit, as PurpleMustang says.
Comment from Mappo on 28 May 2012 at 10:15
I think this is just one example of when mapping at different scales can cause you more work as you return put in more detail than the initial mapping.
Another example is a building being put in as a node, I’ve not noticed any simple way to convert that to a building outline and carry across the data and history (maybe there is, please point it out!).
My general feel is you don’t want to make it more difficult for people to map the areas with low detail just to make it easier for those mapping in extreme detail, you need some kind of balance. And if you can improve tools, then you improve things for both mappers. That also takes work though so you’re trying to balance developers, and mappers at different scales and different experience levels. Basically, it’s a hard problem, so try not to get too annoyed at someone doing it “wrong”.
Comment from Mappo on 28 May 2012 at 10:17
Oh, and where streams and boundaries are colocated, I’ve been putting them in seperately, as the invisible boundaries are imported from an external source and the river can be traced and changes over time without (I think) the legal boundary following it. It’s a bit annoying trying to draw a trace over the top of another without it being automatically joined. Again, better tools seem like the answer.