Chris Morley wrote: >Sent: 24 August 2008 8:51 PM >Cc: talk@openstreetmap.org >Subject: Re: [OSM-talk] Left and Right? > >Karl Newman wrote: >> On Sun, Aug 24, 2008 at 9:53 AM, Rory McCann <[EMAIL PROTECTED] >> Gervase Markham wrote: >> > What's current tagging best practice with things which are to the >> left >> > or the right of a way (e.g. bus stops)? >> > >> > A nearly-approved proposal for a canal-side object has been >> objected to >> > by someone who thinks that the tag should be on a node which is >> part of >> > the canal rather than next to it, with left/right indicated as >> part of >> > the tag key name. >> > http://wiki.openstreetmap.org/index.php/Proposed_features/Mooring >> > >> > Do we do that for any other tags? Do we have >highway:left=bus_stop? >> >> Personally I add the node to left of the way, not as part of the way. >I >> believe the OSM theory is that the way represents the middle of the >> road. So things like mini-roundabounds and traffic lights are part of >> the way (ie road), but a bus stop is off to the side of the road. >> >> A similar thinking is obvious in the Karlsruhe House Address Scheme >> >(http://wiki.openstreetmap.org/index.php/Proposed_features/House_numbers/Ka >rlsruhe_Schema), >> since the buildings that are numbered are not physically in the >middle >> of the road, they are added as nodes to the left or right of the way. >> >> Yes, and that method is not topological, which makes it very difficult >> to associate that feature (bus stop, house number, whatever) with the >> way that it's actually located on. It should either be a node that is >> part of the way, or have a relation to connect the node with the way. > >I think that the topological aspect of OSM's data structure is important >and well worth maintaining in nodes and ways as well as in relations. We >are not just drawing pictures, we are also recording relationships. This >is why the representation of a mooring - a stretch of canal where boats >tie up - as a separate way not connected to the canal seems wrong to me. >In this case and with bus stops or house numbers, if you convey which >side it is on by having a separate node or way displaced an arbitary >short distance to one side, then you lose this side information at lower >scales, when it may still be important to a user. With a topological >description it is still available.
I totally agree on this approach, ie the node is part of the way, but only for features which have direct relationship to each other. This for a bus stop of a mooring I make the node part of the way because these are features that apply and have a relationship with the way itself. For house numbers however I make a separate node. I do this for two reasons, the first is that the house has no relevance to the way it is alongside. We think of house numbers being part of a street but in reality they aren't, they are references for buildings. The second reason is that if we were to add nodes for every house on both sides of the street to every way we would soon find out ways totally unmanageable. As a further reason, houses are normally connected to the street with a driveway/footpath. In a fully featured map you would draw these in eventually. Its these that make the true relationship between building and street. Always try top keep things simple. Keep like with like and don't try to over engineer the result and generally the result will be more than sufficient. > >Left/right are sometimes criticised as being dangerous because they can >be "accidentally" reversed. It is editing programs that do all the >reversing and it would be better if they provided better support. It >would not be difficult to have a scheme with automatic reversal of tags >(on the way or its nodes) containing "left" or "right" or a few others >(like "oneway"), together with a more intelligent warning for the user >in other cases. For bus stops I get around this problem by using a "towards" key. I can then place my node in the way happy in the knowledge that the stop is easily referenced by the direction/destination the bus is travelling. Works a treat in Birmingham because all the bus stop signs have a "Towards" statement on the sign. Cheers Andy _______________________________________________ talk mailing list talk@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk
