[Talk-GB] Secondary, tertiary and unclassified

[Mark Goodge]

On 04/11/2015 08:40, Lester Caine wrote:
> OK finally spotted what is going thanks to the new style sheet ;)
>
> The question is where do we get the 'tertiary' designation from since in
> many cases there is little to distinguish those roads from
> 'unclassified'.

As far as the UK is concerned, this is part of the official 
categorisation. Although we're only used to 'M', 'A' and 'B' appearing 
on signs, the actual classification goes a stage further to include both 
'C' and 'U'. This data is part of the National Street Gazetteer (NSG). 
The NSG is used by commercial cartographers, and is how Google, Bing, 
OS, et al tell the difference between tertiary and residential routes.

If you go to http://roadworks.org and enable the base data layer, the 
underlying classification is exposed and you can click through from any 
road to get its full official classification data. Here, for example, is 
a C road (tertiary) near where I live:

http://portal.roadworks.org/data/dsp_usrnDetail.cfm?r=AAAmziAACAADtFTAAA&lyrType=rstat 


and here's an unclassified (residential) road:

http://portal.roadworks.org/data/dsp_usrnDetail.cfm?r=AAAmziAACAADs0iAAC&lyrType=rstat

Unfortunately, the NSG is not Open Data, so it isn't available to OSM by 
default. The nearest we can do is attempt to visually classify by 
observation. That's one of the weaknesses of a crowd-sourced approach., 
If that matters to you, you might want to get involved in the campaign 
to get the NSG released as Open Data.

Mark
-- 
http://www.markgoodge.com