[Talk-GB] Admin Boundaries and OS OpenData BoundaryLine

[Tom Chance]

On 29 May 2012 17:19, Chris Hill <osm at raggedred.net> wrote:

> They need to be manually entered as relations sharing nodes with those
>> features.
>>
> I would say that sharing nodes can lead to problems. Boundaries that get
> imported or manually traced from OS data often have no visible reference on
> the ground. If you share nodes with something else, when someone aligns
> that something else to aerial imagery, or a GPS trace or whatever, the
> boundary (which was probably right) gets moved too. Why do nodes of one
> object need to be shared when they are quite different objects?


This probably varies according to a number of factors, but where boundaries
are just abstract information coterminous with physical features it makes
sense to me that the objects in OSM share nodes. Many boundaries in urban
areas could just be relations containing lots of roads.

Take the example of someone moving a road but not also moving the boundary.
That introduces an inaccuracy right away. They could also move both but not
bother to get the locations exactly right, say by making the gap between
them larger, getting a kink in the wrong place, or not having them exactly
coterminous. Perhaps they aren't all that interested in boundaries. But
then along another person comes to check if a house is in this or what ward
and they're misled. I prefer to have the boundaries share nodes so that
people are forced to move boundaries with roads/streams/etc. and forced to
break them apart if they really aren't coterminous.

To my mind in these cases boundaries should be treated the same as routes.

Of course if you don't know that a stream and a boundary are supposed to be
related and you go and share nodes because they happen to be in roughly the
same place, then moving the stream to align with a GPS trace obviously
shouldn't move the boundary so you introduce problems.

Regards,
Tom



-- 
http://tom.acrewoods.net   http://twitter.com/tom_chance
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