How to create island in a river using JOSM


I have mapped some roads on an island that does not appear in the OSM database. Using JOSM I see the outline of the island is already mapped using a landuse=name tag, plus a waterway=riverbank tag in a small section, but this does not show up in rendered maps.

How can I convert this into an island? Or how do I create an new island and set it to the same shape? I have uploaded data with JOSM before, but nothing too complicated.



PS. My preference would be to find a manual covering all editing topics that I could read off-line. I find video tutorials are slow to download and limited in what they explain. However I will be happy with whatever answers I may get.


Hi, I am having the exact same problem as the original poster, I hope you don’t mind, Here’s a permalink of the lakes I am having problems with in not showing up on the rendered map.

In mapnik the lake with islands was ok, but I did a little improvement:

Connected the splitted parts of the lake.

Made a multipolygon of the lake.

A matter of taste is, if the lake should be cut out of the nature-reserve area.

Another to-do : There are many roads in this area tagged as highway=road (=unknown road type). Should
be specified to the actual road type (residential? service? track?).


Hi Chris, thanks for the help. Very much appreciated. Had a bit of a read on Multipolygon yesterday, but it didn’t help. I don’t understand it. I have one more island in a botanical garden not far from the link I posted. I mapped out all the walking tracks. It has one island in the middle of the lake, but it to is not showing up in the rendered maps. I will take a look at the changes you done. Hopefully from there I can figure out how to do this.

You should have seen the maps a couple weeks back before I started uploading roads etc. Nearly all the roads where not named. With time all will be named. I’m pretty much on my own out here.

A multipolygon is a special type of a OSM relation. A relation is simply a collection of other
OSM objects (nodes, ways, relations).

Multipolygons are simply spoken polygons with holes. Put the outer bounding ways of the
polygon as “outer” into the relation and the inner bounding ways (the holes) as
“inner”-member. Put the properties of the object (e.g. natural=water for lakes) to the outer ways.

The inner ways don’t need to have any tags, but may have own tags. So, if the hole
is “filled” with scrub, tag is as natural=scrub.