Gluing, Landuse

Posted by mwbg on 16 September 2013 in English (English)

In the area where I'm mapping, I keep coming across ways glued for no apparent reason. I have an intense dislike of gluing, except for when two ways are bound by_definition, such as a County boundary being defined to be coincident with the center line of a river.

Here, I'm trying to add roads to relations, but keep coming up on the situation where the road is glued to two landuses.

Where the two landuses are identical (usually residential), what's the point of having two polygons butted-up to one another (glued) ? Wouldn't it be better if these were merged into one landuse ?

I can understand having separate landuse=residential polygons where they are separated from each other by, say, a road. However, where the (line of the) road itself forms the boundary of both landuses, I can't see the point. Does this hark back to an age when a road was considered to be just a line, of infinite thinness ?

What's the correct way of handling this.

Location: Warndon, Worcester, Worcestershire, West Midlands, England, United Kingdom

Comment from malenki on 17 September 2013 at 19:06

I agree with you that there are situations where gluing landuses doesn't make sense. Sometimes I also merge identical landuses which are side by side. But for some of your examples I have arguments against your reasoning:

  • boundary on a river
    First it would be interesting where the boundary data comes from. When it is imported it is already a bad idea (imho) to glue it to a river traced from Bing since it is likely that the imported data is more exact. The other prolem is: rivers do change. Are boundaries updated by law the same way as the river wanders year by year?
    The quality of aerial imagery changes. Just yesterday I reworked parts of river Osum which had been mapped by using low resolution imagery and now with hi res has offsets from ~100 to 500 meters.

Thus I unglue the ways when I happen to enhance a river and find it glued to a boundary

  • two identical landuses
    can have different owners/operators or different names.
    It is also possible that the tagging of one of them just recently got changed.
    </nitpicking> ;)

PS: to select a way from a bundle of glued ways, in JOSM use middle click and hold the list with ctrl.

Comment from mwbg on 17 September 2013 at 19:21

malenki: I was being a bit hypothetical in my original post. The specific problem is that I am mapping bus routes (relations) on existing roads.

For one thing, it's very difficult to get at the road (in JOSM) because it's glued to (in this case, another instance of the same road, and) to two landuse boundaries.

In practically every case, the adjoining landuses are residential, as are the roads going through it/them.

As far as I can see, there are two intepretations, and the gluing that I am seeing doesn't match either:

I suppose my question is: does the road inherit the landuse of those polygons through which it runs, or does it have its own landuse (as yet, undefined).

In the first case, the centre line of the road should form no (glued) part of either landuse, and the two landuses should be merged.

In the second case, the two landuses should be separate, and end at the road margins.

In all the above, I'm assuming that the landuses are identical, have no other different tags.

Comment from malenki on 17 September 2013 at 19:47

Why are two roads glued together..? (link?)

For the rest: I'd assume Bing Imagery can give enough reason to glue landuse to the highway. In earlier times (of bad imagery) I did this, too, partly - and now I unglue that stuff again.

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