[Talk-GB] Multiple coincident boundary nodes. Data quality issue ?
colin.smale at xs4all.nl
Fri Aug 11 21:04:13 UTC 2017
not sure I would call it a real data quality issue, but it "could be
There are two coincident lines, which share some nodes but do not share
the majority of nodes, despite the fact they are coincident.
One line represents the boundary of Great Britain, and the admin
boundary of Highland.
The other line is the boundary of "Loch Sunart to the Sound of Jura
Marine Protected Area"
If the nodes are coincident by design, then they should be shared. If
they are only coincident by accident, then not. In this case it is
likely (but I don't know for sure) that the MPA boundary is effectively
defined in this area as "the boundary of Highland Council" so the nodes
could/should be shared.
Nodes contained in a way do not normally have, or need, tags. However,
where a point feature occurs in the course of a way, then the "by
accident/by design" distinction applies again. A pedestrian crossing is
often a node in a highway: this is "by design" because the position of
the crossing is irrevocably linked to the position of the highway. But
sometimes nodes for things like monuments could be added without having
zoomed in properly, with the editor choosing to re-use an existing node
instead of creating a new one. So my reaction to your statements b and c
is "it depends".
On 2017-08-11 22:07, Mike Parfitt wrote:
> If I put Drimnin in the centre of my tablet's screen in an area of 780m EW and 515m NS (landscape) the land/sea boundary is marked (not always accurately) by a number of coincident way/relation/multipolygon items all of which pass through 49 things that look like nodes.
> There are actually 71 individual nodes (see caveat) of which :-
> 27 nodes are on all of the way/relation/multipolygon items
> 44 nodes are arranged in 22 coincident pairs, each on a subset of the way/relation/multipolygon items
> At least one of the nodes in each coincident pair has a tag, but the 27 nodes that are on all of the way/relation/multipolygon items do not have any tags.
> CAVEAT : I haven't checked every one of the 49 things that look like nodes, so it is possible that some may be composed of more than 2 coincident nodes. Even if they are all just pairs of nodes, I don't know if the same subset of the way/relation/multipolygon items occurs throughout.
> I am limited to contributing updates via an Android tablet - using Vespucci, as iD is unuseable on my touch screen.
> I can easily move the 27 nodes that are on all of the way/relation/multipolygon items, but for the others, I have to select and move each of the coincident nodes individually - to the same location !
> My opinion is that :-
> a) boundaries should have their properties defined at the way/relation/multipolygon level
> b) individual nodes on such boundaries should not have any tags
> c) coincident nodes on such boundaries should be combined into one
> What does everyone else think ?
> How should the right solution be implemented ?
> Talk-GB mailing list
> Talk-GB at openstreetmap.org
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