[Tagging] How to tag named group of named water areas?

Dave Swarthout daveswarthout at gmail.com
Mon Oct 8 09:48:13 UTC 2018

The multiple water body situation arises frequently in my Alaska mapping. I
have struggled over the years to tag them in such a manner that the names
will render but without resorting to trickery to make that happen. A couple
of years ago I happened on a group of three lakes, two of which contained
islands and were already multipolygons created during an old import. The
other was merely a small lake. The USGS Topo maps I use as my guide for
naming things in these remote regions gave the name Three Lakes to the
group. I created a multipolygon relation tagged with natural=water to
contain them but for reasons I do not recall now, put the name Three Lakes
on each of them. Perhaps I was struggling to get those names to display
inside JOSM, or maybe it was just because I had so little experience with
multipolygons of this type. Whatever. I made a note to myself to check
after a time to see if Three Lakes was findable via a Nominatum search. I
did that last week and found that they were not.

So I retagged them this time assigning the name "Three Lakes" to the
relation containing the lakes and removing it from the individual lakes. I
checked back again today, after a few days had elapsed, and was able to
seach for and find Three Lakes. But also today, when I was checking the
area in order to use it as an example for my reponse to this thread, I
noticed that two of those lakes have individual names. I added the names
but JOSM complained. Of course, it wanted something more than just a name.
I added water=natural to each of those two lakes and was able to upload
them successfully. So now my lakes are tagged with natural=water twice,
once on each of their outer ways and once in the relation. If the
natural=water tag is removed from the relation, the simple lake doesn't
render as water. Where is the proper place for the natural=water tag?

I fool around with the tagging every time I create one of these monsters.
Just last week I created another multipolygon relation to hold a pair of
calderas named "Twin Calderas", one of which contains a lake. I searched
for it today and found it but another mapper had edited it in order to "fix
old style multipolygon". I asked him in a changeset comment what exactly he
had done to fix it and he replied, "The old-style multipolygon (with only
type=multipolygon tag) with the two members on the left (one outer and one
inner) was removed, the correctly tagged multipolygon was updated to also
include the inner from the other multipolygon, because it also includes its
outer." I'm reluctant to ask him to explain further because I'm clearly
confused by his answer and indeed, by the entire concept.

I'll be following this thread closely to see if I can learn anything from


The Three Lakes relation is id:6,714,525
Twin Calderas relation is id:8,771,446

On Mon, Oct 8, 2018 at 3:08 PM Martin Koppenhoefer <dieterdreist at gmail.com>

> sent from a phone
> > On 7. Oct 2018, at 21:46, marc marc <marc_marc_irc at hotmail.com> wrote:
> >
> > I'm not sure it's necessary to create a value to repeat the type of
> > object already present in osm. otherwise it would require a value for
> > each type of object and a value for each type of possible combination
> > between theose types.
> what is “necessary” has to do with the use case someone has in mind, if
> you want to unambiguously map that there is a group of lakes with a common
> name for the group, it is indeed necessary to describe the thing with more
> tags than just a name.
> Cheers, Martin
> _______________________________________________
> Tagging mailing list
> Tagging at openstreetmap.org
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Dave Swarthout
Homer, Alaska
Chiang Mai, Thailand
Travel Blog at http://dswarthout.blogspot.com
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