[OSM-talk] New "Highways" view in OSM Inspector

[edodd at billiau.net]

>
>
> I'm aware of the concept that the earth is not flat.
>
> But... This is a two dimensional map. IFAIK there is no 3d data. The PoV
> of viewing the OSM data via the likes of Mapnik is always through the
> surface of the earth to the centre of the earth. Therefore a line such
> as this Oz highway is, when viewed in a map, going to be straight.
>


ah, not exactly
depending on your projection and its distortions (all projections have
distortions) a straight line on earth can be represented as a curved line
on a map.
Eg Air navigation east coast north america to europe.
This is long enough that shown on a Mercator projection the straight line
which the pilot flies is shown as a curve - because in 3D it is a curve.
It is known as a Great circle.
http://mathworld.wolfram.com/GreatCircle.html
"A great circle becomes a straight line in a gnomonic projection "