----- Original Message -----
From: "Andrew Harvey" <[email protected]>
To: "Nick Hocking" <[email protected]>
Cc: <[email protected]>
Sent: Thursday, February 02, 2012 10:46 AM
Subject: [talk-au] Mapping Coastlines (Was: Re: Boundary removal.)
On Thu, Feb 2, 2012 at 11:22 AM, Nick Hocking <[email protected]>
wrote:
I tried remapping some coastline down near Eden, from
Bing imagery. This works well buit is very time comsuming
and the coastline is BIG and probably Bing imagery does
not cover it all at the necessary resolution.
I suggest we get back our old state natrional boundaries
from before ABS and then improve them over the next year
or so, at our leisure.
I'm curious about how to map the coastline from imagery? The coastline
is meant to be mean high tide, but with all those waves coming in and
only a rough guess of where abouts in the 12 hr cycle the imagery was
taken how do you know where to put the way?
With the high resolution imagery its usually quite easy to differentiate
between permanently dry areas, and areas which was been covered by water in
the last 12 hours.
Having said that, tropical regions where there may be large areas of
mangrove etc, it is quite common for the coastline way to be drawn at the
mangrove / water interface rather than the mangrove / land interface .
This boundary is usually quite visible on even the low resolution imagery.
If all else fails, then you have guess when to put the coastline, someone
with more knowledge can always come along later and correct it. If its a
choice between no coastline, and inaccurate coastline then I'd always go for
inaccurate. You could always tag the ways with a fixme if you wanted to
flag them up.
Lastly, if you are redrawing coastline ways then can I make a reminder that
the direction of the way is important. They must be drawn with the water on
the right hand side.
Regards
David
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