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<p>Hi,</p>
<p>There are still some problems with verifiability of objects
geometry. This has been discussed lately here:<br>
</p>
<p><a class="moz-txt-link-freetext" href="https://github.com/gravitystorm/openstreetmap-carto/pull/3750">https://github.com/gravitystorm/openstreetmap-carto/pull/3750</a></p>
<p>but we came to the conclusion that this is not the best place to
go with fundamental problems, so I come here to talk about tagging
strategies.</p>
<p>Christoph (imagico) has proposed there a set of example rules
that he believes are self evident and invited to challenge them if
someone disagrees, so here I am:<br>
</p>
<ul>
<li>polygons are a way to geometrically define a two dimensional
entity through (and only through) an explicit delineation of its
one dimensional boundaries.</li>
</ul>
<p>I agree with that. That's why area mapping for bays is good as
long as you have a source for this. This is what we do with admin
borders - we get the nodes that we know and simply link them. Or
we use some data from authorities. No matter what source do you
use, there can be disagreement (look at admin borders problems
which are not solved to this moment, yet we don't simplify admin
objects into nodes or lines because of that).<br>
</p>
<ul>
<li>for the decision what kind of feature to use to represent a
certain real world feature in the OSM database mappers should
put mapping and data maintenance efficiency above perceived
desires of data users. The main criterion should be how to most
efficiently represent verifiable information on the feature in
question without storing either redundant or non-verifiable
data.</li>
</ul>
<p>Written rule does not support this interpretation, it's short and
clear. Data maintenace is not a rule, is not mentioned there even
as an excuse or exception and of course is not higher level rule
than verifiability. On the other hand people commonly use nodes or
lines for representing areas. <br>
</p>
<p>There is simply a clash between written rules and the common
usage. It's the open question how should it be solved.<br>
</p>
<ul>
<li>there is no principal connection between the nature of a real
world object and how it can or should be represented in OSM
above the mapping efficiency criterion previously mentioned.</li>
</ul>
<p>I don't agree here. There can be some simplification used (just
beware of oversimplification, especially for bigger objects), but
this is always worse than lack of simplification.<br>
</p>
<ul>
<li>straits between concave coasts are one dimensional entities,
they have a width but they have no length.</li>
</ul>
<p>I see no support for this claim, so I completely don't agree with
it:</p>
<p>- "Most commonly it is a channel of water" (Wikipedia, strait) -
channel has length and width<br>
</p>
<p>- "The shortest distance across the strait, 33.3 kilometres"
(Wikipedia, Strait of Dover) - the mentioned thing is only a part
of the strait, not the whole entity</p>
<p>- "A narrow area of water surrounded by land on two sides and by
water on two other sides." (description on the OSM wiki)<br>
</p>
<ul>
<li>the verifiability of a node location representing a feature
exclusively depends on if multiple independent placements of the
node converge to a single location. This is a completely scale
independent problem meaning variance of different placements can
be anywhere from less than a meter to hundreds of kilometers.
This has no bearing on the principal verifiability.</li>
</ul>
<p>This sentence is very complex, I'm not sure what do you think.<br>
</p>
<p>When you have 4 different limits of the Gulf of Guinea for
example (
<a class="moz-txt-link-freetext" href="https://commons.wikimedia.org/wiki/File:Limites_du_golfe_de_Guin%C3%A9e-fr.svg">https://commons.wikimedia.org/wiki/File:Limites_du_golfe_de_Guin%C3%A9e-fr.svg</a>
), you will have 4 different central points which don't converge
at all (the distance between the middle of A and D is roughly 1000
km), so using nodes does not help anything. At best one can put it
in the A area as the common part of all of them, but this is
indirectly choosing A area as proper, which is just hiding the
problem, not getting rid of it.<br>
</p>
<p>The solution would be for example to ask local people from all 12
countries if they think this part of the coastline belongs to the
bay and take their claim above what others (non-local people) say.
At best, it will give you properly sourced shape. At worst, you
may not get the consistent answer - then you might just simply not
map it at all.<br>
</p>
<p><br>
</p>
<pre class="moz-signature" cols="72">--
"I see dead people" [Sixth Sense]</pre>
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