Creating lakes with islands

Well, I’m relatively new to OSM and this question has probably been asked before but I can’t seem to find an answer in the forum that satisfies me. so here it goes: I’m trying to edit a lake to include island polygons within it. When selecting the polygons to try to make them a multipolygon I am faced with the following message: “These features can’t be merged because at least one hasn’t been fully downloaded.” I have no idea how to resolve this issue. Pleas advise.

Generally it helps to include a link to the object you are referring to, to name the editor you are using, but, at face value, it would appear that you haven’t selected a large enough download area to fully include one of the items probably an existing relation, that you are trying to work with.

In Josm:

  • download the whole lake from OSM, not only parts.
  • select the coastline of the lake and the coastline of the islands
  • press Control-B for something like “create Multipolygon”


in Potlatch: don’t know

in iD: forget it. iD is not for working with relations


ps: may be, you need the utils2plugin for Josm

Hello, I’m afraid you have compounded the first mistake many times. The lake polygon (a single way outline) is now made up of nine multipolygons each with between one and seven members. Some of the islets (again single way outlines) are somehow made of several multipolygons each.
I don’t think you can repair this in the iD editor, you’ll just make it worse. Would you like me to fix it for you?

BTW you’ve done the same thing with a couple of your buildings (building way one outline, courtyard one outline, multipolygon is one outer and two or three inners).

hadw - I’ve been using the in-browser editor. The approximate coordinates are 21.1170/85.6090.
wambacher - I haven’t the slightest clue as how to download the entire lake. Can someone enlighten me so I know for next time?
BCNorwich - yes please! I’d appreciate it if you fixed it!

again: don’t try it with iD.


I fixed ist (includung buildings with a yard inside south-east of this lake).


Many thanks to all!