[talk-au] Mangroves and coastline

[David Groom]

----- Original Message ----- 
From: "Stephen Hope" <slhope at gmail.com>
To: "OSM Australian Talk List" <talk-au at openstreetmap.org>
Sent: Thursday, December 27, 2007 12:05 PM
Subject: [talk-au] Mangroves and coastline


>I was looking at the top of Cape York, where the current coastline in
> OSM ends.  I was comparing the PGS coastal data with the current OSM
> data and a yahoo image of the current coastline, and notices that the
> data seems to be out by several kilometres.  Finally I realised that
> the PGS data is following the dry land border, whereas the current
> data in OSM is following the outer edge of the mangrove swamps.
> Normally this is not a major difference, but here there were
> differences of up to 12 km.
>
> Are there any guidelines as to which we should use? I guess it depends
> on your definition of the coast. I can see arguments both ways. If we
> decide to use the outer mangrove edge, then we should check the PGS
> data in Qld even more than normal, because of the reefs and large
> mangrove beds behind them in places.


In Cairns & Darwin areas, I have marked the coastline as the outer edge of 
the mangrove swamps. (ie at the mangrove / clear water interface), but kept 
the PGS outline at the land / mangrove interface removed the tag 
natural=coastline, and tagged an area as natural= marsh.  (maybe not the 
best tag, but currently there is no natural=mangrove_swamp, so it appeared 
to be the best compromise).

Sadly neither the Mapnik or osmarender layers currently render natural=marsh 
(i have put in request for both to do so, but to no avail), but you can see 
what the rendering would look like at

http://wiki.openstreetmap.org/index.php/Image:Cairns.png

http://wiki.openstreetmap.org/index.php/Image:Darwin.png

David


>
> While I'm thinking of it - are we interested in mapping the Great
> Barrier Reef? (or any other reefs for that matter?)  Permanently dry
> islands, sure.  But what about the low-tide only areas, or those that
> are just below water level all the time?
>
> Stephen Hope
>
> _______________________________________________
> Talk-au mailing list
> Talk-au at openstreetmap.org
> http://lists.openstreetmap.org/cgi-bin/mailman/listinfo/talk-au
>