[Tagging] Additional detail of Levee mapping via embankments
joseph.eisenberg at gmail.com
Mon Nov 18 02:15:49 UTC 2019
> for straight embankments, cuttings, slopes, if they are done with an area
> that shares nodes, then I don’t think you need a relation.
Agreed. You can map the area of the cutting or embankment as a new tag
like man_made=embankment_area or similar, and the area would include
the same nodes as the man_made=embankment or =cutting line.
It would also be possible to map the area of an embankment or cutting
this way when the central highway line is tagged as embankment=yes or
cutting=yes: it would be inside of the area and this clearly relates
the area to the highway.
Previously I mentioned using an area for levees/dikes, and there was
some concern that this would be difficult for really long
This is the same situation as with river areas: we tag these by
breaking up the area of the river into reasonable-sized chunks, maybe
a kilometer or two long, and the linear waterway=river line is also
broken into 10 kilometer lengths so that it is easier to edit without
conflicts. I would use this same technique to map the area of a very
1) Map the central line as man_made=dyke, or highway + cutting=yes /
embankment=yes as relevant. This line should not be 100 kilometers
long, but a reasonable length: probably no more than 10 kilometers,
and even shorter in a major city.
This step is enough for most uses. You don't actually have to do steps 2 or 3.
2) If you want to, you can map the top line of any man_made=embankment
lines, if desired.
3) Finally (this part is very optional), you could map the area of the
cutting or embankment or dike as a series of closed ways. Don't make
them more than a kilometer or 2 long, since it's a pain to edit them
if they are too huge. It's better to use a few smaller closed ways
rather than a huge multipolygon to map complex features with holes.
(We should not use a new tag like man_made=levee for this, because
"levee" is American English for "dike", so it would be better to use
man_made=dyke_area or something similar.)
See the examples at Tag:waterway=riverbank for how this would look.
There seems to be some confusion about the need for a relation. But
notice that rivers do not use a relation to combine all of the areas.
There is a type=waterway relation but this is only for the central
waterway=river lines, and it is not not commonly used, because in
practice database users can put the lines back together by just
looking for river ways which have the same name and meet at a shared
Similarly, database users can fairly easily recombine all of the
waterway=riverbank areas which make up a river into one big polygon if
they need to do this for rendering or data analysis for some reason
(but usually it's not needed). This could also be done for any
`man_made=dyke_area` closed ways which are touching, if someone wants
to make a polygon including all of the levees along a certain river in
Tokyo or something like that.
- Joseph Eisenberg
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