[Tagging] Map a divide?

Kevin Kenny kevin.b.kenny at gmail.com
Thu Oct 4 14:46:19 UTC 2018

In some maps that I render, I want to show the divide between a couple
of major river basins. (I have a good DEM for the area in question and
can derive the line readily.)

In light of the recent thread on topographic prominence, I wonder if
this is sufficiently interesting information at least to push it to
OSM. (If not, that's fine, I have a PostGIS database and a bucket of
shapefiles and know what to do.)

If it is sufficiently interesting, the question then arises: how to map/tag it?

'natural=ridge' comes to mind, and the divide in question has a local
name. (The 'Catskill Divide' separates the basins of the Hudson and
Delaware Rivers.) This approach appears to run into problems, as I
read the Wiki. I see:

> The way should connect saddle points and peaks, and the arrows should point upwards.

That may be all right for a ridge ascending the flank of a single
mountain, but what I'm talking about is the spine of a range, with the
ridge traversing dozens of named peaks. Even with a single mountain,
if there are false summits, the arrows on a single way cannot point
upward all the time! (And the wiki is clear that the

Do I misread, and should the reading instead simply be that the
arrowhead should be higher than the arrow tail? In that case, I could
break the divide into two ways, with a common endpoint at the highest
summit in the range.

Consider this a low-priority item. I have (or will have - there is a
bit of debugging yet) the data. I know how to render them. I'm happy
enough with a shapefile or a private PostGIS table if others aren't

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