Islands within multiploygon lakes JOSM how to required

OpenStreetMap Questions and Answers
#1

Hi

I am gradually building up my knowledge of OSM and have swapped from Polatch 2 to JOSM, kicking and screaming. I by reading up now can create lakes using multipolygon relationships to get over the 2000 maximum node limit. I also within a simple lake can create multiple islands (place=island) and form a multipolygon inner relationship. But I am stuffed if I can achieve the same feat with multipolygon lakes with islands.

Here is what I attempted to do. Created a lake from multiple ways and joined them as a multipolygon relationship and in the relationship used “name=Lake Trevallyn”, “source=GPS/Bing”, and “natural=water”. I then draw in the island and used on the way (not the relationship) “place=island”, “source=Bing”. Then figured out how to select all the ways used in creating the multipolygon lake and added in the island. Brilliant I thought as I had six outer and one inner. But when I went to upload I received the error message “No style for multipolygon (1)”. Figuring that maybe that the issue was on applying properties to the way rather than the relationship I remove the properties from the island way and applied them to the mulitpolygon relationship for the island but still got the “no style” error message. Also regardless what I tried the island, in JOSM, at least did not change from the colour blue.

Ok while not the most stylish guy around I would at least in JOSM get the matter sorted as I am working on my next step in mapping my bushwalking areas by adding islands to the multipolygon lakes I have created. I thought I would practice in a urban area that I kayak first as it needed to TLC.

Anyway help as always appreciated. I find OSM help rather cryptic including the web stuff and maybe the help could add a little howto as JOSM is not intuitive at times. Still get confused with using shift rather than control to select multiple ways in JOSM and even the way of moving around at times but getting better with JOSM.

Cheers

#2

Hello Ent,

Two problems, one how to rectify what’s now mapped, two how to do it easier next time.

One, you now have two multipolygon relations one tagged fully including the name Lake Trevellyan Road, (I take it the Road should be included), but no island. I would keep this relation and add the island to it. Bring up the relation edit box, select/highlight the island then add it to the relation, (click one of the Add arrows). Delete the relation that does not have the lake name. That should put things right. I do see that you don’t have a land cover key/value tag for the island. This is not necessary for a multipolygon I just wondered if it was an over sight.

Two the easiest way to make multipolygons in JOSM, create all of the areas, (including nested ones, (holes in holes in holes)) place all appropriate tags. Select/highlight all areas at the same time, (hold down “Ctrl” click on all items), then from the “Tools Menu” click on “Create Multipolygon”. Bring up the relation editing box and check all is OK, inners and outers marked properly.

I think JOSM is well worth the extra effort involved but agree it is lacking in friendliness to put it politely.
Regards
Bernard

PS Just read your post again, I think the reason the island is not changing colour is mainly because of the lack of land cover tag.