[OSM-talk] Landuse areas etc. abutting highways

Apollinaris Schoell aschoell at gmail.com
Sun Oct 4 21:27:18 BST 2009

On 4 Oct 2009, at 12:42 , Mike Harris wrote:

> I'm seeking advice as to best practice in the following type of  
> situation:
> As an increasingly common example, now that people are getting  
> around to mapping areas such as leisure=, natural= and landuse= ...
> Consider the case of landuse=farm on one side of a highway (say a  
> secondary road) and leisure=golf_course on the other side of the  
> highway. The easiest way to map this - and the one usually adopted  
> it seems - is to make the boundaries of the farm and the golf course  
> both coterminous with the highway so that the three lines are  
> superimposed in the editors (not quite sure how the various  
> renderers handle this) and the representation of the highway has  
> zero width.
> There are, however, potential problems with this (quite apart from  
> the slightly clumsy editing when several ways are superimposed)  
> where detailed mapping would ideally show that in real life the golf  
> course and the farm do not in fact have a common boundary but both  
> are, for example, separated by hedges (which may or may not be  
> mapped) from the road.
> It is clearly possible to map the farm and the golf course as  
> separated areas with the road mapped as a line drawn between them -  
> i.e. the mapping has three separate parallel lines. This assists  
> with mapping more clearly features such as junctions of paths with  
> the road (and stiles on paths at such junctions). But is this unduly  
> messy or does it create rendering issues (e.g. if the lines are not  
> absolutely parallel and just far enough apart to render with random  
> gaps between, say, the golf course and the road.
> The situation is even trickier where, say, a farm has been mapped as  
> a single area (same land use) with, say, a road crossing it -  
> whereas in practice, this is two separate farms - one on each side  
> of the road - that may at some stage need to be named separately.  
> Then we have to go back and split the area, etc.
> This seems to be a quite a generic issue and I am wondering how  
> people see the pros and cons of (a) the simple approach with  
> coterminous lines giving a notional zero width to the highway, vs.  
> (b) the more precise approach of mapping the areas either side of  
> the highway as areas that are separate both from each other and from  
> the highway.
> In practice, almost all mapping seems to use approach (a) - but  
> would approach (b) be easier for subsequent editing and addition of  
> detail, and rather clearer as it avoids superimposed ways and  
> potential editing errors?

a) is common but bad practice, very difficult to edit and not really  
correct when it comes to micro mapping. the road is not part of the  
farm or golf course
If you don't want to do micro mapping the best approach is to create a  
multipolygon relations for the farm and one for the golf course. use  
the portion of the highway in the polygon as outer way and delete the  
duplicate ways.
b) is nice if you really have precise data, this matches what's on the  
ground and can be extended easily with more details

from rendering point of view both are same if the distance between the  
parallel lines is short enough. highways are typically rendered wider  
than whats on the ground and will fill gaps caused by not perfectly  
parallel ways. also the version with relations is well supported

> Views?
> Mike Harris
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