OpenStreetMap

Island problem

Posted by mapryan on 7 August 2012 in English (English)

All

I've been doing a lot of mapping around Narathiwat in Southern Thailand. I had the coastline running into the bay in the city and it seemed to make more sense to cut the sea off at the mouth of the river and convert everything from there backwards to be river (and with riverbanks instead of coastlines). However, since doing that, the islands in the rivers have now all become blue and are not appearing on the map.

I figured it was something to do with the direction of the ways, but I tried changing these to no effect.

Is there anyone more experienced in these things could have a quick look and maybe work out what I'm doing wrong

Cheers

Mike

Location: ถนนบ้านค่าย-อ่าวมะนาว, Narathiwat, Narathiwat Province, Thailand

Comment from AndersAndersson on 7 August 2012 at 21:45

Islands should not be tagged with waterway=riverbank since they are not made of water. I used a multipolygon to define the riverbank and the islands. You can take look if you want to see how I did.

I wonder about the administrative relation. http://www.openstreetmap.org/browse/relation/903822 Should that really be on the river?

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Comment from mapryan on 8 August 2012 at 10:07

Thanks for that. The administrative relation was there before I started so I can't really comment on that

Just so I understand - by multipolygon does this mean that there are multiple objects that relate to each other? I'm not really sure I understand the concept, but I can see what you did on the map. Is there a webpage that easily explains this?

Cheers

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Comment from AndersAndersson on 8 August 2012 at 14:31

In a way they relate to each other, but I would say that one of the reasons to use a multipolygon is that they do not relate.

For example, if you are in a playground in a park, you are still in the park (no multipolygon needed). But when you are on an island in a lake you are not on the water any more. So then I would use a multipolygon to define that the surrounding area is water, but everything inside the island is not water.

Have a look at http://wiki.openstreetmap.org/wiki/Multipolygon

Regards

Anders

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