W dniu 15.05.2015 18:33, Martin Koppenhoefer napisał(a):
the area tag is sort of a special tag, it is used as a geometry flag
to say whether a closed way is linear or a polygon.
That is how we are used to think about it, but it's just a convention.
If you flip the point of view, you can say area is one of a most basic
GIS objects and it means we have a filled polygon with some additional
properties and functions probably (like name, school or highway), and
one very special exception (value "no" is rare - 1,67%) telling it's a
closed line (probably also with some properties).
It is strange, I agree, but still useful, coherent and no worse than
building=no (0,01%, so also marginal, but useful and coherent too).
For many types of objects area=* is so basic, that we don't even use it
explicitly unless we need to tell something is different this time. And
it's also highly conventional, because no highway is a line in reality,
it's always an area, but it just happened we started OSM with routing in
mind (big and middle scale) rather than micromapping (micro scale) and
to make things easier we assumed that closing the highway line by
default means "area=no".
I think it was a clever move, sparing us additional typing and storage,
but still in reality area is a basic concept with some exceptions,
rather than special property of GIS objects.
--
"The train is always on time / The trick is to be ready to put your bags
down" [A. Cohen]
_______________________________________________
Tagging mailing list
Tagging@openstreetmap.org
https://lists.openstreetmap.org/listinfo/tagging
