[Talk-ca] Using Canvec data to recreate or modify coastline features

James A. Treacy treacy at debian.org
Thu Sep 8 18:58:33 BST 2011


Daniel,
I'd like to make this more concrete with an example. If you have canvec data
that shows:
      llllllllllll      this area is land
    -i-i-i-i-i-i-i-i    way which is natural=water;water=intermittent
      iiiiiiiiiiii      area with intermittent water
    -w-i-w-i-w-i-w-i    boundary with 2 ways. One is natural=water and
                            the other is natural=water;water=intermittent
      wwwwwwwwwwww      this area is water

is this what OSM should have?
      llllllllllll      this area is land
    -c-i-c-i-c-i-c-i    boundary with 2 ways. One is natural=coastline and
                            the other is natural=water;water=intermittent
      iiiiiiiiiiii      area with intermittent water
    -i-i-i-i-i-i-i-i    way which is natural=water;water=intermittent
      wwwwwwwwwwww      this area is water

Obviously, the ways would be closed but I think this gives the idea.

On Mon, Sep 05, 2011 at 09:37:11PM -0400, Daniel Begin wrote:
> Hi all,
> 
> Earlier today I was looking at coastline features modified to fit Canvec
> data and I found a problem with the "conversion". I think all of those who
> are converting coastline using Canvec data should be aware of the Canvec
> water data model...
> 
> In Canvec data you will find two types of water polygons (natural=water)...
> 
> One type defines permanent water - an area that is always covered by the
> water. 
> 
> - It is tagged natural=water
> 
> One type defines intermittent water - an area that is occasionally, but not
> always covered with water.
> 
> - It has two tags. One is the standard natural=water tag, the other is
> water=intermittent tag(1).
> 
>  
> 
> The problem is that the coastline seems to be defined as the mean high water
> level (MHWL) position(2). To create a coastline that meet the MHWL position
> using Canvec, you must merge all natural=water polygon type before
> converting it to coastline.
> 
>  
> 
> JOSM provides a good tool to merge those polygons - join overlapping area
> (Shift-J)
> 
>  
> 
>  
> 
> Daniel
> 
>  
> 
>  
> 
>  
> 
> 1 - http://wiki.openstreetmap.org/wiki/Proposed_features/Water_cover
> 
> 2 - http://wiki.openstreetmap.org/wiki/Tag:natural%3Dcoastline and other
> wiki discussions
> 

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-- 
James (Jay) Treacy
treacy at debian.org



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