[talk-au] Mapping Coastlines (Was: Re: Boundary removal.)

David Groom reviews at pacific-rim.net
Thu Feb 2 12:43:45 GMT 2012



----- Original Message ----- 
From: "Andrew Harvey" <andrew.harvey4 at gmail.com>
To: "Nick Hocking" <nick.hocking at gmail.com>
Cc: <talk-au at openstreetmap.org>
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 <nick.hocking at gmail.com> 
> 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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