[OSM-dev] One value per key? Why not one pair per object?

Frederik Ramm frederik at remote.org
Mon Feb 2 02:44:37 GMT 2009


Stefan de Konink wrote:
> What is the motivation to go to the one value per key thing again. 
> Opposed to unique(objectid - key - value)?

As a client programmer, I say that unique keys make everything simpler 
for me. It is much easier to check whether "the highway tag has a value 
of X" that it is to check whether "one of the highway tags has a value 
of X". I'm basically shifting some of my burden onto the mappers 
("please make up your mind what kind of highway you're tagging").

If two people each implement a renderer that draws cycleways in blue and 
footways in red, then it is very likely that an object tagged 
"highway=cycleway" and "highway=footway" will show up blue on one map 
and red on the other. It is even possible that the same renderer will 
sometimes draw it red and sometimes blue...

Key uniqueness robs us of some cool things but we get simplicity in 
return which is a price worth paying in this particular case, I think.


Frederik Ramm  ##  eMail frederik at remote.org  ##  N49°00'09" E008°23'33"

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