Trouble with creating islands

Posted by JuLn on 7 May 2019 in English (English)

Hello mappers!

I've recently installed JOSM. It indeed makes mapping a lot easier. However I don't understand how to create islands. When I try, they don't render correctly, so I assume i'm doing something wrong.

I have an example: I'm currently trying to create two islands in a huge river: Topech Island, and Notchien Island. If I remember correctly, I created the coastline on JOSM, created a multipolygon and then went on the ID editor to tag the multipolygon as Island.

However, the islands aren't showed on the map, only their names are. What did I do wrong?

Thanks and happy mapping!

Comment from MOI N on 7 May 2019 at 06:36

Try just using iD

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Comment from Aiki on 7 May 2019 at 09:34

You need to make the ways that form the islands inner members of the Kojitech River relation. The renderer will “understand” that these areas are out of the water.

By the way, the Kojitech River relation being riverbank should not be named. For the river course itself, draw a way, either in the middle of the river or its thalweg if it’s really offset. Tag the way name=Kojitech River and waterway=river. The name will then appear along the course of the river and not in the centre of current Kojitech River area.

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Comment from LemonKing on 7 May 2019 at 09:48

Don't put a type=multipolygon tag in the island way itself. In stead, include the island way into the existing riverbank relation which you already tagged as type=multipolygon. Then specify the island way's role in the relation as "inner".

In iD, this can only be done if the rivebank and island are close enough to fit into the area you zoom into for editing. All existing relations within the editing area appear in the "all relations" options below the tagging section.

An island in a lake or a river is always part of a the same multipolygon as the water body. However, an islands in the sea is not part of any multipolygon relation and is tagged as natural=coastline. In both island types, the way runs anti-clockwise and should be carefully closed.

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Comment from Aiki on 7 May 2019 at 13:01

In addition to what I said, keep the island relations as they are so that their names are still rendered as islands: black and italic font. It is the “only” purpose for such relations apart from being used for area calculation.

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