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

[Frederik Ramm]

Hi,

Anthony wrote:
> I'd imagine for some applications we'd want the former (a straight 
> road/rail), and for some we'd want the latter (the border of Wyoming).  
> Which should be the official definition according to the specs?

Because very few people in OSM have any formal training in geography or 
cartography, it is very likely that most mappers - having the standard 
slippy map in mind - will assume that a straight line on Earth is a 
straight line in the Mercator projection, whereas most programmers will 
not hesitate to make the assumption that a line from (100,100) to 
(80,80) will pass through (90,90). *Both* of these assumptions are 
different, and *both* are not the true shortest surface path (geodetic 
or "great circle").

Even if there were an "official definition according to the specs" (ha, 
ha), it would be ignored by the majority of people (who simply wouldn't 
think that far). Because of that, it is a very pragmatic choice to say 
"let's not have distances of more than a few kilometres between nodes" 
because that will then reduce the error between the three different 
types of "straight line" discussed above to something very small[*].

I think 1km is fine, 5km is acceptable, 10km is stretching the envelope 
and anything above that is asking for trouble. OSMI highlights distances 
of, I think, 0.3 degrees or more, which translates to roughly 30km at 
the equator, or more than 20km in Australia or more than 10km in 
northern Canada. Anything highlighted by OSMI is very likely to not show 
up on tiles at home maps, and also very likely to not be downloaded when 
people download an area for editing in any of the popular editors.

Bye
Frederik