[OSM-talk] Landuse areas etc. abutting highways

Chris Morley c.morley at gaseq.co.uk
Tue Oct 6 15:45:48 BST 2009

Mike Harris wrote:
> Thanks to those who responded to this thread. Advice gratefully received.
> There seems to be a clear majority preference for option (b)
> - the more detailed approach that avoids superimposing boundaries
> of areas (and their nodes) on an adjacent way (and its nodes). 
> I fully understand the two caveats:
> 1. It is only worth being precise if there is precise data available.
> 2. There are a few exceptions where, for example, the character of the
> adjacent area has access features more like that of a normal linear way
> - the pedestrian area is a good example.
> I am persuaded that the advantages of forward compatibility and a higher
> standard of mapping justify my small efforts (where I have good GPS data)
 > in separating out superimposed areas/ways and using option (b).
 > I am particularly pleased to receive support for splitting single large
 > landuse areas (e.g. =residential or =farm) that cross large numbers 
of ways.

Let me encourage you to use option a), based on the reasoning of 
Frederik Ramm.

In detailed mapping, everything is an area way which share nodes with 
its adjacent areas. When roads etc. are linear features, it means they 
have *indeterminate* width and the only non-arbitrary representation 
of this in an editor is for the width to be zero, with adjacent areas 
on both sides sharing the nodes - option a). This makes it consistent 
with the detailed modelling approach. I would look at the linear road 
etc. as being, not a centre-line, but an indeterminately wide 
structure comprising the road surface, sidewalks, verges etc. up to a 
boundary (which in the British countryside would often be a hedge.) By 
mapping with option a) you are saying that the golf course, say, comes 
up to the road's boundary hedge but that you haven't specified exactly 
where that is. If you do know, you are into a detailed mapping 
approach. If a linear road is still used then it would now be 
interpreted as a centre-line, as is sometimes done with rivers.

Since I map in the same are as you, I suspect that in most cases you 
do not have enough information to use the detailed mapping approach. 
Even with arial photography we have available, poor resolution and 
interference from tree cover and shadows often does not allow the 
separation between the hedges to be very reliable.

Editor support for ways sharing nodes is certainly poor, but as with 
inadequate renderers, we should improve them rather than adding 
artificial data (arbitrarily positioned structures) into the database.

Landuse areas which cross a large number of ways are very common. 
Surely you don't intend to divide say, Delamere Forest, into a large 
number of separated areas separated by the paths and tracks? When you 
do need to do it, separating an area into two at a road is certainly 
laborious and maybe somebody should build a JOSM plugin to do it.


>> -----Original Message-----
>> From: Martin Koppenhoefer [mailto:dieterdreist at gmail.com] 
>> Sent: 05 October 2009 15:52
>> To: Marc Schütz
>> Cc: talk at openstreetmap.org
>> Subject: Re: [OSM-talk] Landuse areas etc. abutting highways
>> 2009/10/5 "Marc Schütz" <schuetzm at gmx.net>:
>>>> 2009/10/5 "Marc Schütz" <schuetzm at gmx.net>:
>>>>>> But a) could be used as acceptable temporary solution until 
>>>>>> someone with better information (like having aerial 
>> photography) 
>>>>>> remaps it as
>>>>>> b)
>>>>> Yes, this is basically what I wanted to say. Leave it to the 
>>>>> mappers
>>>> whether they want to use a way or an area for a road.
>>>> it will be much harder to add this detail, if all areas 
>> are merged though.
>>> Not really. JOSM supports disconnecting ways since a long 
>> time now. But anyway: doing things wrong just to make editing 
>> easier is not a good thing.
>> +1. That's why adjacent landuses (see topic) shouldn't be extented to
>> the center of the road.
>>>>> But with option (b) and a linear way you would have a 
>> gap next to 
>>>>> the
>>>> road. In the case of landuse, this is not a problem in 
>> practice, but 
>>>> if there is a place, there you need to insert artificial ways that 
>>>> are not there in reality, just to get the connectivity 
>> between the two objects:
>>>>> http://osm.org/go/0JUKytHID--
>>>> which objects are you referring to? parkings usually have 
>> those ways 
>>>> (for crossing the sidewalk) so they won't be artificial, and 
>>>> pedestrian areas are the exception I mentioned above.
>>> Look at the google sat image:
>> http://maps.google.com/maps?f=q&source=s_q&hl=de&geocode=&q=bayreuth&s
>> ll=37.0625,-95.677068&sspn=59.856937,107.138672&ie=UTF8&hq=&hnear=Bayr
>> euth,+Bayern,+Deutschland&ll=49.946316,11.577148&spn=0.000754,0.001635
>>> &t=k&z=20
>> That's the mentioned pedestrian area. I agree with you here.
>>> Mapping it the way it is done there does not really make 
>> sense: Either the exact geometry is important for you, then 
>> you should convert both the plaza and the road to areas. Or 
>> it isn't, but then there shouldn't be a problem with 
>> extending the plaza so that it borders to the road.
>> +1. but that's still pedestrian areas / highway areas. In these cases
>> the areas _do_ connect to the road.
>> cheers,
>> Martin
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