On Tuesday 03 June 2014, Martin Koppenhoefer wrote: > > As a sidenote I wanted to point out that there are currently already > 281547 ways (I suspect most of them to represent areas) tagged with > place=* (not much compared to a total of 3.1M places in OSM) which > could serve as an alternative to your (preprocessing intensive) > process if more mappers could be convinced for this concept of > mapping settlement extensions.
Note many of those are islands, see: http://taginfo.openstreetmap.org/keys/place?filter=ways#values And the others - like Frederik said - are most likely not really describing the actual builtup area. > The main problems of your approach --- it is still only "guessing" > and the derived dataset might have a high probability to identify > "built-up" areas but it will not in all cases be able to tell which > settlement an area belongs to and it is a ressource intensive process > that reasonably cannot be done on the fly --- could be overcome with > explicit place polygons. On the downside it will of course take us > quite some time to manually map all those settlements, and it is not > even clear if people are interested in general to map this kind of > feature (in addition to landuse etc.). If the main style picked this > up and rendered areas with > place=(city,town,village,hamlet,isolated_dwelling) as "built-up-area" > this would surely help promoting the cause ;-) I think i'd disagree here. place=city|town|... is simply not a well defined area. You might think you can draw a line around any settlement in the world but there is no way to say where exactly this line is to be in a verifiable way. So if you start mapping this everyone will draw it differently and nothing is gained in the end. What i do is essentially defining the builtup area as the area where the density of roads and buildings exceeds a certain limit. This in itself is no guesswork at all - the base data is of course very variable and there are a lot of subjective choices involved in the process that follows. You might feel inclined to adapt this density measurement as a rule for manually mapping areas with place=* but keep in mind measuring object density is always specific to the scale you look at and there is no natural scale of settlements you can base this on. -- Christoph Hormann http://www.imagico.de/ _______________________________________________ dev mailing list [email protected] https://lists.openstreetmap.org/listinfo/dev
