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

Daniel Begin jfd553 at hotmail.com
Tue Sep 6 02:37:11 BST 2011


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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