[Tagging] natural=bay as nodes are evil

Ilpo Järvinen ilpo.jarvinen at helsinki.fi
Mon Oct 27 20:04:45 UTC 2014

On Mon, 27 Oct 2014, Martin Koppenhoefer wrote:

> 2014-10-27 17:37 GMT+01:00 Christoph Hormann <chris_hormann at gmx.de>:
>       But this is exactly what does not work with a hand mapped
>       polygon either
>       since the edge of the bay is not well defined.
> it will work in most cases, and only give questionable information when you
> are close to the fuzzy end towards the open sea (or another bay). In these
> cases there won't be a correct answer from a human either, because it simply
> isn't clear where that border is.

IMHO, the most controversial thing in this all is that the approach 
Christoph is proposing would require us to not map natural=bay but 
"natural=bay_entry" instead, and that is obviously exactly where the fuzzy 
part is. That is, a mapper would be forced to place bay nodes into the 
place where nobody can say for sure if it's in the bay or not.

Otherwise his algorithm would obviously end up failing because of arbitary 
picked threshold that makes lots of assumptions about the shape of the 
bay. The main assumptions are about width of the bay and depth at the 
nearest coastline that is not in the either extreme of the bay. Consider 
e.g. a very wide bay which has two pockets but at the middle you have some 
penisula extending towards the bay entry and thus also towards the bay 
node. But it would certainly work in many cases just fine like most of 
the algorithms tend to do (of course, assuming we'd map bay_entry instead 
of bay).


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