[OSM-talk] Changes to Key:access wiki page

[Christiaan Welvaart]

On Tue, 25 Aug 2009, Aun Johnsen (via Webmail) wrote:

> On Tue, 25 Aug 2009 10:47:14 +0200 (CEST), Christiaan Welvaart
> <cjw at daneel.dyndns.org> wrote:
>> hi,
>>
>> On Sat, 22 Aug 2009, Tobias Knerr wrote:
>>
>>>> I listed :backward and :forward postfixes for access keys
>>>
>>> What you are doing here seems like picking raisins from conditional
>>> tagging and trying to handle it as a special case. I'm not sure whether
>>> you are aware of my proposal?
>>>
>>>
> http://wiki.openstreetmap.org/wiki/Proposed_features/Conditions_for_access_tags
>>
>> I didn't really answer this question yet. My idea with :forward and
>> :backward was to group all access restrictions - keys that take
>> yes/no/destination/private/etc. - with the access key. So I also
> sometimes
>> write e.g. access:vehicle:forward=no . But time restrictions should also
>> be included, e.g. as :T<from>-<to>, so one could write (crazy) things
>> like:
>>
>>    access:vehicle:forward:Tmo-fr=destination
>>    access:vehicle:forward:Tsa-su=yes
>>    access:vehicle:backward:Tmo-fr=delivery
>>    access:vehicle:backward:Tsa-su=no
>>
>> A problem with oneway= is that it cannot accept the whole range of access
>
>> values - only yes/no. So the above cannot be done with :oneway AFAICT.
>>
>> (max)height/weight/width/speed could maybe also be included with access,
>> but I think it is better to treat them as "access limits" and keep them
>> separate. Then the conditions proposal looks good for these keys.
>>
>>
> When you are getting this complicated on it, maybe it is better to handle
> this in relations? This way each special condition can be handled
> separately without cluttering the map with tags. A road can have a set of
> general access tags, and than use relations for the complicated access
> conditions, such as psv only on school days, goods delivery 10-12 mon-fri +
> 11-12 saturdays in july, destination for taxies exept saturdays after 22,
> and so on. That will allow you to do all these special condition without
> access:vehicle:forward/backward.
>
> I havn't seen that complicated access restrictions in the areas I map, so I
> have no need for it, but I know that reality is a little different in
> Europe.

I guess using relations is an option. But AFAIK the vast majority of roads 
in the world only needs a highway tag for access, and most specific access 
restrictions are simple. My example was not really practical, if such 
complicated restrictions exist they are likely rare. This would mean that 
an access restriction relation needs a completely new specification that 
will not be used much, while the system I described scales from simple 
situations to quite complicated ones. Also, having access restrictions in 
two locations (tags on the way/node and in relations) only complicates 
things.


     Christiaan