I’ve got a small question: how should I map an area (“leisure=common”) which is surrounded by a street? Should I connect the nodes from the area with the nodes from the street, or leave a tiny gap between them? The latter seems better, as it’s easier to edit and rendered correctly (without gap), whilst the former is mocked about by JOSM’s validator. I have however come across some cities where it has been mapped by merging the nodes, which is why I ask the question.
I am anxious to hear the answer to this one.
I have been using the nodes in existing ways to create areas which JOSM’s validator complains about (overlapping way with areas or some such). So far I have ignored that particular complaint because the way and the area are defined as two seperate objects (they just share a few nodes). I also haven’t found the right bit of documentation to explain this… and its ramifications, if any.
The way represents the centre line of the street.
As the area next to it does not go up to the centre line of the street, it should be drawn where it is physically located, ie with a gap to allow for the width of the street.
Hmm okay, that is one answer, draw it the way it is… but, JOSM will complain if the way is a fence which has no width to speak of and defines the boundary of that same area. It will also kick up about two areas sharing nodes along a common boundary.
So putting aside drawing correctness, is there anything wrong with sharing nodes (ie overlapping an area and a way or overlapping two areas) from an OSM DB technical point of view? Is it going to screw with anything in the DB?
Vclaw, do you draw each and every residential block in a larger residential area individually so that every street has that gap that you speak of to allow for the road?
No, the db has no notion of spatialness or any other relation between ways. You can happily share nodes between umpteen areas, and the OSM db wouldn’t care less.
Thanks, so some JOSM complaints (in context of this discussion) can be safely ignored?
It’s probably not even JOSM per se that complains, but the Validator plugin. You can disable some validator checks, if they bother you, or they give too many false positives.
But yes, you can still upload even when the validator complains. If the API doesn’t accept your data, you’ll know soon enough.
You’re right it is the validator. I don’t consider the warnings (they’re never in the “warning” category anyway - and I always fix those) a false positive in the sense that it is reporting something that it isn’t part of its design. Disabling it is not really an option because I also use that particular check to ensure consistency in what I have done… even if I am consistently wrong… and that is the part that bothers me.
Perhaps some of the validator warnings are based on the authors (of the plugin) preferences and mapping style.
OK, so I understand that roads are centrelines, not representing the full physical width of the road. I’m not sure, however, that creating a parallel set of nodes for an area way is any better of a practice. In my experience, I see people making the area nodes too far inwards as they try to maintain a physical separation. The end result is no more accurate than if the nodes were shared, and probably less so. (It also renders poorly which is a secondary consideration, but worth mentioning)
What is the community opinion on creating areas using the road nodes in a multipolygon and assigning the landuse tag to the relationship instead of to the polygon? Is this considered acceptable or even best practice?
I prefer, when mapping an area adjacent to a road, to share all the nodes. To my mind, if there is a gap, what is in the gap? It can sometimes make editing difficult but more often it can make it easier, if you need to move a road, you only have to move one set of points as the adjacent areas are attached, whereas if the areas are separated, you have to move three lines of nodes.
It’s a long-standing controversial issue, but my opinion is that areas should end at the edge of the road surface, not at the centreline. To answer the question what’s in the gap: The road, of course. With rivers, you wouldn’t connect these adjacent areas to the central waterway=river way either, but rather to the riverbank outline, right?
As for placing the area boundary nodes too far inwards, that only happened here before we had decent aerial imagery. Now these area boundaries are usually drawn pretty accurately along the edge of the road surface.
From a practical point of view, the disadvantages of areas sharing way nodes tend outweigh the advantages. Yes, there is an advantage when moving roads, but in my experience you don’t do it all that often, and even then moving two sets of nodes independently isn’t actually that much additional effort. For me, it happens much more often that I need to split/merge road sections (for example because I want to add more tags and these apply only to a part of the road). There was a mapper around here who has connected landuse and amentity areas to roads a lot, and now that I’m starting to add lane and sidewalk tagging to these roads, this is getting really annoying.
I guess that if you insist on connecting areas to the road centreline, then multipolygon relations might be less of a burden on those who edit these roads than closed ways with shared nodes. I prefer to avoid both, though.