[Tagging] length=

[Mike Thompson]

> E.g.: a 17-degree mapped mountain road or San Francisco street's will get
> its actual length a 5% bonus compared to its real-life counterpart.

True, but such roads are not very common (17 degree ~= 30%). There are
a few short streets in places like San Francisco that are this steep.
In these cases if someone actually went out and measured them with
suitably precise equipment it might make sense to have some sort of
length tag, but I would suggest something to differentiate it from a
purely horizontal measurement. Of course, you could also drape the OSM
data over a suitably detailed DEM (digital elevation model) to get
your answer as well.



> Depends on the accuracy
> you need, mostly for analysis purposes.

If you need that level of accuracy you may want to consider data
sources in addition to OSM.