[Tagging] Points instead of areas

Christoph Hormann osm at imagico.de
Tue Aug 7 13:24:47 UTC 2018

On Tuesday 07 August 2018, Daniel Koc4‡ wrote:
> > A word regarding tolerance of coordinates and the implication that
> > they should be or have to be within the tolerance of measuring
> > devices - i don't think this is or should be the case.  The point
> > of verifiability in OSM is not a tolerance threshold, it is if
> > multiple independent determinations converge to a single data
> > point.  Standard deviation of that might be 50m or it might be
> > 500km.  If you ask a thousand mappers to position a place node for
> > Africa and 90 percent of them place it in or around the Central
> > African Republic you have a verifiable mapping IMO.
> The placing of points is always inaccurate this way or another, just
> as all the approximations. Well, for flagpoles that might be good
> enough from human point of view, but most of the objects have easily
> visible shape and size that one can measure (with GPS or with a plain
> measure tape). Building, country, pitch, bench...
> [...]

I think you have not understood the difference between measurement 
tolerance and convergence here.

In any case how geographical objects that can be verifiably mapped in 
principle are best represented in the OSM database is a matter of what 
is most efficient, most convenient and least prone to errors *for the 
mapper* (and not the data user!) to document the verifiable information 
available about the object in question.

For a bench for example you could:

* map it with a node with tags like direction, width/seats, depth, 
height, backrest etc.
* map it with a linear way (would need to be orientation sensitive which 
is kind of error prone)
* map it with a closed way outlining the bench geometry (plus direction 
tag since the closed way is not oriented)

For a plain rectangular footprint bench (>99 percent of benches) there 
is absolutely no difference in the achievable level of accuracy and 
detail in the representation of reality between these three variants.  
But there is an immense level of difference in efficiency and 
convenience of these representations for the mapper.

Any argument beyond that (like that there is something inherent about 
benches (or populated places or continents) that makes them more 
suitable to be represented as X in the database) is usually just stuff 
made up to convince mappers to map in a certain way for the convenience 
of certain data users.

Christoph Hormann

More information about the Tagging mailing list