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#1 2008-03-20 16:53:02

daniel
Member
Registered: 2007-08-04
Posts: 2

mapping holes in an area

Hello,

In my local area I have a lake with an island in the middle and this is causing me a couple of problems.

Firstly I read the wiki:
http://wiki.openstreetmap.org/index.php/Elements#Area

To map "holes" in a area, e.g a clearing in a wood, first create ways-segements in one direction around the outer edge of the area, then draw a pseudo-edge from the outer edge to the hole und create way-segements around the hole in the opposite direction, then follow the pseudo-edge a second time, this time in oposite direction back to the outer egde. If there is a second hole, just interupt your rounding the first hole and create a second pseudo-edge from the first hole to the second hole, then circle the second hole, go back over the pseudo edge to the first hole and continue as decribed above.

Now it might just be because i'm dyslexic, but that to me isn't even English.

Can someone explain this concept a little more clearly? (images would help me, if you have the time!)

Also second issue, I know if it's an island I need to use "natural=land" but it's also got allot of trees on it, so ideally i would like to do "natural=wood"... can i do both? I read somewhere that you can double up by doing "natural=land;wood" does that work and render well? or should i just do "natural=wood"? or maybe two layers?

Thanks for any help you can give me!

- Daniel

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#2 2008-03-20 17:11:02

Ben
Member
From: United Arab Emirates
Registered: 2006-05-23
Posts: 213

Re: mapping holes in an area

It isn't particularly clear but I think what it is saying is to create a 'polo' shaped object, make a 'C' shape, where you go around one way, then go inwards and back around the other way to mark the inside.  Then to make it a 'polo' make the 2 sections of the 'C' where you turn around so close that they use the same nodes.

By psuedo edge I think it's referring to the wood itself, rather than a pseudo edge for the osm-data, which is rather confusing.

For lakes though I thought just drawing an island with natural:land; layer:1 would work

<edit> 2nd Question:

Natural:land;wood won't render, and seems a messy way to go.  You should either just make the island just natural:wood, or make a wood on the island (separate way) tagged natural:wood again, or make 2 ways on the same circle, one tagged natural:wood, the other tagged natural:land

<edit2> A diagram

A. 2 ways..
B. A C shaped wood
C. Shift the edges of the C shape together

makingawood.png

Last edited by Ben (2008-03-20 17:49:09)


Ben

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#3 2008-03-20 17:54:45

daniel
Member
Registered: 2007-08-04
Posts: 2

Re: mapping holes in an area

Excellent, thanks for your help! much clearer now.

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#4 2008-03-20 18:20:18

Ben
Member
From: United Arab Emirates
Registered: 2006-05-23
Posts: 213

Re: mapping holes in an area

I've changed the description on the wiki page you linked to.  Please check it and edit it if you feel it still makes little sense from your perspective.


Ben

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#5 2008-03-20 18:30:10

Harry Wood
Member
From: London UK
Registered: 2007-05-29
Posts: 147
Website

Re: mapping holes in an area

Then there's this Relations/Multipolygon concept which seems to be tackling the same problem, but I'm not sure if any renderers look at that data yet.

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#6 2008-03-21 00:40:55

emj
Member
From: .se (59.3N17.99E) 0735969076
Registered: 2006-06-18
Posts: 949

Re: mapping holes in an area

@Harry Wood.

I think they do, there are some beautiful multipolygon houses in Helsinki.

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