[Tagging] natural=bay as nodes are evil

[Christoph Hormann]

On Tuesday 28 October 2014, moltonel 3x Combo wrote:
>
> That's actually a very nice rendering. The channels in particular
> seem to be oriented very naturally. But when I look at the underlying
> osm data (nodes), it is much less clear how those features are
> oriented. I feel like the rendering tricked me into thinking "that's
> it, the channel is laid out this way" when the actual data says
> nothing of the sort.

For a channel between two islands with simple convex shape the situation 
is actually much clearer than for a bay - it is a one-dimensional 
feature, it has a width but no length so mapping it as an area is 
plainly wrong.  In more complicated situations the established method 
is to use a way connecting a few key points - up to extreme cases like 
here:

http://www.openstreetmap.org/way/163242449

> I admit I don't fully understand how your algorythm works. I can't
> imagine how you reduce everything to nodes and still retain
> information about orientation and curves. Can you change your
> rendering to display the infered polygons instead of the name ?

I do not infer any areas, i just generate curves (splines) based on the 
nodes and the surrounding coastlines and place the text along them.  
The main problem is that spatial database systems are not well suited 
for this kind of work (i.e. tasks like 'find the closest coastline in a 
certain direction').

-- 
Christoph Hormann
http://www.imagico.de/