[Talk-GB] Estimating coverage

[Peter Miller]

On 19 Jul 2009, at 12:44, Frederik Ramm wrote:

> Hi,
>
> Peter Miller wrote:
>> There is a relation for 'London Boroughs'. I wondered if we should  
>> produced one for 'Regions of England', and 'ceremonial counties of  
>> England' and add the appropriate relations to them.
>
> Generally, relations that just serve the purpose of collecting  
> things are frowned upon. Relations are not meant to be a substitute  
> for categories.
>
> http://wiki.openstreetmap.org/wiki/Relations/Relations_are_not_Categories
>
> For example, you would not do a relation "buildings by Norman  
> Foster" because that can be simply done by adding a tag  
> "architect=Norman Foster" to the buildings. If "Regions of England"  
> is exactly a collection of relations with a certain admin level and  
> location, then it carries no extra information and should not be  
> created. (Rule of thumb: If you feel the desire to run a script that  
> would automatically add and remove things to/from a relation based  
> on their location and tagging then your relation is probably a  
> collection relation that does not add value.)
>

Ok, thanks for that Frederik. You never know who will be on a list!    
One limitation of OSM at present is that the category=Region_in_Engand  
doesn't work if one also wants to tag the same relationship as  
something else, for example as 'administrative county in England' or  
as 'ceremonial county in England' or anything else. So would it be  
appropriate to tag it as 'Region_in_England=yes'?

> Having said that, it's all evolution, and if people really feel  
> there are advantages to using relations as collections then there's  
> probably nothing I can do against that ;-)
>
>> Here is the 'London Boroughs' relation as an example. I like the  
>> map that is produced from it.
>
> Yes, I have the impression that people often do collection relations  
> because they enjoy being able to simply request a relation/full OSM  
> document from the API and retrieve all the objects, rather than  
> having to find a working XAPI server and formulate a query. However  
> this is *really* something that should be done at search time and  
> not in the database - if we had grouping relations for everything  
> that someone possibly wants so search for... hm, ok, the "slippery  
> slope" argument doesn't help.

What is good about relations is that a thing (way/relation) can be  
part of many other things and there isn't another neat way of doing  
that in OSM (other than using tag=yes where 'tag' is the category  
name). Possibly that is good enough, but if so then it should be  
outlined on the 'relations are not categories'  page and it would of  
course be good to have a way of displaying all relations which match a  
search string. Should we suggest that the 'Footways in East Anglia',  
or more usefully 'long distance footpaths in England' should be tagged  
as 'long distance footpaths in England'=yes.

Here is the Wikipedia category:
http://en.wikipedia.org/wiki/Category:Long-distance_footpaths_in_England


Regards,




Peter


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