[Tagging] new access value

Richard ricoz.osm at gmail.com
Thu Oct 8 13:43:15 UTC 2015

On Thu, Oct 08, 2015 at 12:07:43PM +0200, Colin Smale wrote:

> All this data is aimed at routing and navigation, not being a source of
> detail for the use of judges. 

sure, routing is the main aim. So how can we do that?

variant 1 - current approach:
#1 mapper sees a sign on ground
#2 mapper guesses how to possibly translate this "no tricycles with
   more than two zombies on board" sign to OSM permissions and the way for 
   which the sign is valid for
#3 router looks at country specific defaults (not that any router I know
   would actually do that?)
#4 router combines tagging with defaults

variant 2 -tag traffic signs on the ground:
#1 mapper tags sign exactly as is
#2 router looks into country/area specific table of signs and defaults 
   and tries to do something sensible with that.

variant 1 served us quite well for years but has these problems:
* translation between sign on ground and persmissions can require local or
  even expert knowledge by the mapper
* meaning of most signs can be changed by legislature anytime - suddenly the
  "designated footway" forbids or allows horses/skates/skis

variant 2 requires more complete mapping (suffering from leaking graphhs 
problem) but has some advantages:
* easier verifiability on the ground
* the difficult sign->meaning translation can be improved/updated anytime without
  changing every single way that was mapped the old way
* even the most exotic signs can be mapped

> The idea of having area-specific defaults has been discussed before, and
> AFAIK didn't get formalised. 

not easy but would be nice 


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