[OSM-newbies] What's the easiest method to "snap" an area boundary to adjacent ways?

[Samat K Jain]

On Friday, August 27, 2010 02:22:45 pm m902 wrote:
>   I have a few situations where the boundary (or part of it) of an area 
> is an adjacent way. Examples are:
> - A sports field, bounded by a river on one side and a road on another.
> - A residential area bounded by a road on one side and the sports field 
> on another.
> - A commercial area bounded by a road.
> Obviously I could draw the boundary by selecting each node of the 
> adjacent way...but I wondered if I am missing somethng and if there is 
> an easier method?
> I would like to just select a beginning node and an end node on the 
> existing way and tell it to set the area boundary to follow it.
> Is anything like that possible?
> Couldn't see anything like that in Potlatch or JOSM.

Best practice is to NOT have ways share nodes unless there's an actual 
intersection.

Why? Well, after you've created such a thing… try to select and edit it. Yeah, 
it's a pain. No editors make it easy (though I've found Potlatch makes the 
most easy).

Two alternatives:

(1) Draw a parallel way, with its own nodes.

This is "correct" if you want to be philosophical and think about the 
abstractions maps represent… the way representing a road is supposed to be the 
centerline for the road. If you're sharing the nodes with another way, that's 
implying that the boundary of that area (commercial zone, residential area, 
etc) extends to the centerline of the road. In all jurisdictions I'm aware of 
this is legally untrue (the same does not apply for administrative boundaries, 
however). If you take a look at well-mapped areas of OSM, this is typically 
what others do.

(2) Create a relation, making the way a component.

Regarding the philosophical viewpoint above, this makes a way part of a 
boundary, which I believe is legally true in certain situations. E.g. the 
middle of a road may actually mark two different counties/states/etc. Using a 
relation is probably preferred but much more work.

It's also worth pointing out that there was a discussion on the tagging list 
'Tagging "natural" borders' a few days ago, and the consensus was for larger 
borders (like countries), don't do (2) because it still makes editing 
difficult.

Regards,
Samat

-- 
Samat K Jain <http://samat.org/> | GPG: 0x4A456FBA

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