[OSM-talk] Is it land or sea: how to map a swamp?

Stephen Hope slhope at gmail.com
Wed Jul 9 02:27:26 BST 2008

The northern coast of Australia has many Mangrove marshes at river
mouths, some of them extending many kilometres away from the dry shore
line.  PGS shows these areas as sea, because they are not dry land -
and that is were the coastlines would have been imported from.  Note
that "being submerged for half the year" doesn't mean the trees are
covered with water, just the mud under them.  The tree tops would be
above water all the time, I suspect.

We've (mostly) tagged them as land, with the coast being on the sea
side of them.  Technically they may be water covered (or partially
water covered, usually about 6 inches deep), but if you can't swim or
boat in them and plants and trees grow there it's land as far as I'm
concerned.  They certainly are not ocean.  Marshes in the UK are also
treated as land from the coastline point of view, even were they edge
an ocean.

See http://www.openstreetmap.org/?lat=-16.9642&lon=145.7843&zoom=13&layers=B00FTF
for an example near Cairns.  More examples are further up the coast.


2008/7/9 Alan Millar <am12 at bolis.com>:
> I came across an interesting area which I don't know how to map or tag.
> http://www.openstreetmap.org/?lat=22.066&lon=89.047&zoom=9&layers=B00FTF
> This is the Sundarbans mangrove forest on the border of India and
> Bangladesh.  The map doesn't look like much, but look at the map with
> aerial photos like in Potlatch edit mode and it starts to get interesting.
> I read that it is submerged for up to half of the year.  The Yahoo aerial
> photos clearly show the forest areas, so I assume they were taken at a
> low-water period.  Google Maps shows it as land.
> Our oceantiles file has it as land, but our coastlines treat it as sea.
> Our coastlines stop at the farmlands which border it.  During the high
> water period, I suppose our coastlines make sense.
> Does anyone have any recommendations of how to treat an area like this?
> Any similar geography already mapped somewhere?  Thanks
> - Alan
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