"Distance" is a poor choice of word in English
The previous definition, saying that "distance" means "Distance of a relation ...", was not comprehensible in English. Distance must be between two places. A single thing such as a road cannot have a "distance". It can have a length, or an "extent", but only a distance from something else.
In the International Standard for RDS-TMC (Radio Data System -- Traffic Message Channel) traffic events can have a length, and also an extent. They cannot (by themselves) have a distance. They can have a distance away from a driver, but this is only meaningful when we say from where the distance is measured. In this case it appears from usage that this "distance" is to be measured between the road's start and end points.
This suggested definition still leaves certain issues undetermined. Lots of roads have breaks or jumps where they are not defined. They disappear at these gaps and then reappear elsewhere. How does the "distance" of a relation handle these gaps? Are the missing km somehow included or are they ignored? ̃
meters or kilometers
"the value is assumed to be in kilometers" Sure ?? i read meter here: https://wiki.openstreetmap.org/wiki/Map_Features/Units
- Sure. As stated there, if not explicitly defined, the unit would be meters. However, here the unit kilometers has been explicitly defined for the key "distance". --Biff (talk) 01:15, 15 December 2013 (UTC)
Extent / length
If we want to map traffic signals we have to be more specific, because we can have the two possibilities. E.g.: We have a bend so far 1000m (distance) and of "duration" (extent? / length?) of 1000m. So we need other key: extent or length ?