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Hi all!

I want to map a small lake. It is fed by some small brooks that I have yet only identified one of. Those brooks are not important, I just mention them here to state that the lake is no bog itself, but fed with fresh water.

The lake is surrounded by reed, which itself is surrounded by boggy meadows, which formely might have formed the shape of the lake itself. That former shape is not in question either, I just mention it here to show that I want to map all three layers (lake, reed, bog) of the area. This is important as it is a protected area that allows several animals to breed, live and actually survive. Showing that it consists of several surrounding areas seems important to me.

How can I achieve this in OSM? I know how to map houses, streets and the like, but with a bog surrounding a reed area around a lake I'm somehow at a loss: The main name of the area is "Eglsee" (near Abtenau in Austria), so I don't want to call the outermost multipolygon of the bog "Eglsee, but only the lake as such.

But when I do so, and I place the lake inside the reed/bog multipolygon area (each of which I could create nameless, just naming the lake itself "Eglsee"), the lake lies inside the reed/bog area, which simply is not right, as the underlying multipolygon would cover the lake then.

So, anyone helps me out with declaring a small lake inside a reed area inside a bog area without declaring all the borders twice and third?

Thanks in advance,


PS: This is the region in question, without any edits from me, for sure: View it in jOSM with layer enabled to see what I want to achieve. :)

PPS: In the above mentioned, unedited version, the lake is tagged as a bog, which in fact it isn't, and it is named "Egelsee", which is wrong, too.

asked 27 Aug '13, 01:11

RobKehl's gravatar image

accept rate: 0%

This is not too difficult. It is, as your question tags suggest, a matter of using multipolygon relations. (Assuming that each component completely surrounds the others.)

Draw three closed ways for the lake, reedbed and bog. The lake can be tagged directly, natural=water, name=Eglsee. I find it particularly useful to add source tags to the remaining ways which will be part of relations.

Now create a relation, type=multipolygon, and add the innermost way (Eglsee) with role inner, and the middle way, role=outer. Add natural=wetland, wetland=reedbed, as tags to the relation. Repeat the process with the outer two ways, but use wetland=bog (I suspect from your description, wetland=marsh, might be more appropriate).

The two wetland areas will render the same way, but the data will be there.

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answered 27 Aug '13, 05:47

SK53's gravatar image

SK53 ♦
accept rate: 22%

edited 27 Aug '13, 15:52

neuhausr's gravatar image



Thank you very much, now I got it to show correctly:

It's changeset 17545301:

Visit that lake, it's beautiful :-)


(27 Aug '13, 22:38) RobKehl

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question asked: 27 Aug '13, 01:11

question was seen: 6,786 times

last updated: 27 Aug '13, 22:38

NOTICE: is no longer in use from 1st March 2024. Please use the OpenStreetMap Community Forum