[Tagging] gross weight - conclusions & changes

[martinq]

> Do we really need 2 tags, maxgrossweight and grossweight? What is the
> difference?

- maxgrossweight is a key
- grossweight is no key. It is a property used on the right side of 
conditional restrictions, for example to express a speed limit that only 
applied to vehicles with a certain gross weight.

Same as: maxlength/maxheight/maxwidth (key) vs. length/height/width 
(property in conditional restrictions).

> IMHO you can assume that maxweight is about the actual weight (this is
> for 4 years on the wiki:

Discussion gave me a different impression. The issue is that the wiki 
page did not make people aware that different weight types exist. 
Therefore I - and also other people on this list - assume that maxweight 
has been used for anything that looks like "a weight" limitation.

Additionally, be aware of your regional bias: If I look for example at 
this page:
http://wiki.openstreetmap.org/wiki/Road_signs_in_the_United_Kingdom
both signs ("No goods vehicles exceeding maximum gross weight" and 
"Maximum weight") are suggesting maxweight for gross weight limitations.

It does not matter how many people have used this specific page: It just 
demonstrates that the author of the page - working with the best 
intentions - came to another conclusion. And if there is one author, 
there will be mappers too.

> [...]Obviously mappers that notice the problem will correct it, where
> grossweight (maxgrossweight) was intended but maxweight was tagged.
>> Only gradual replacement by new & more precise tags and the
>> recommendation to use the new tags instead of the inaccurate
>> 'maxweight' [deprecate maxweight] makes sense.
> -1, I'm against burning a well established and defined tag just because
> on one other recent wiki page there is a problem in the examples
> section. Better correct that contradiction.

It is well established, but sadly used in for different weight types, 
which makes it useless for data users: maxweight=5.5 can mean completely 
different things now. If it was for vehicle weight, I can pass with 5t 
truck + 5t trailer. But if the mapper meant gross weight, then I cannot 
pass with my unloaded permissible gross weight 7.5t truck...

We cannot redefine the meaning and hope that people start checking every 
maxweight sign (how do people know that it has already been checked?).

The only clean way is to deprecate maxweight, inform people why its no 
longer recommended to use it -- and the good reasons for doing this. 
This makes it possible to distinguish between "old" and ambiguous weight 
limit and the new limits with more precise meaning in the future.

I cannot agree that 'maxweight' is "burned" simply because we deprecate 
it: The maxweight definition on the wiki and maxweight tag will remain 
in the database for many years. But we should stop adding more ambiguous 
'maxweight' tags and start a gradual replacement of old 'maxweight' tags 
with their more meaningful counterparts.

martinq