[OSM-talk] Misclassified roads

elvin ibbotson elvin.ibbotson at poco.org.uk
Thu Jul 10 09:06:24 BST 2008

> From: Steve Hill <steve at nexusuk.org>
> Date: 9 July 2008 15:36:03 BDT
> To: talk at openstreetmap.org
> Subject: [OSM-talk] Misclassified roads
> Following the approval of the highway=road tag, I've set about  
> aggressively changing a lot of the highway=unclassified roads  
> around Swansea, that I believe are misclassified, to highway=road,  
> with the intention that they can then be surveyed and reclassified  
> correctly.

If you believe they are wrongly tagged (I would avoid the word  
"misclassified" when referring to an unclassified road ;-) presumably  
you have a good idea what classification they are, so why not just re- 
tag them as primary, tertiary or whatever?

> However, after starting to do this, I've realised just how many of  
> the roads are misclassified - I'd estimate that well over 80% of  
> the roads tagged as highway=unclassified are, infact, not  
> unclassified roads.

How on earth did you arrive at this figure? Wouldn't 'guess wildly'  
be a better verb than 'estimate'?

>  So I'm wondering about the merits of changing *all* the  
> highway=unclassified roads in the area to highway=road so that the  
> whole lot can be classified appropriately from scratch.

No way! I personally have mapped hundreds of roads, a high proportion  
of them unclassified (and I suspect I am not the only one who knows  
what this means) and would not want anyone 'aggressively changing' them.

> This would make it obvious which roads really are unclassified and  
> which need to be checked.
> What are peoples' views on this?  I imagine that much of the OSM  
> world is affected in the same way, and this renders the  
> highway=unclassified tag relatively meaningless in it's current  
> state.  Should there be a global reclassification to fix this, or  
> is there a better way?

There's always a better way. I suspect the motorway/trunk/primary/ 
secondary/tertiary/unclassified hierarchy was derived from Britain's  
highway classification system, since it appears to be a perfect match  
and OSM's roots are here. I don't have much knowledge of how roads  
are classified elsewhere, but I guess most countries have  
classification systems which can be made to correspond to this  
hierarchy. The grey area for me is in the tertiary/unclassified/ 
service/residential area. C-class roads in the UK are not labelled as  
such on road signs or maps (and of course we shouldn't look at maps  
as this might infringe copyright ;-) so if you don't work for the  
local highway authority you can only guess at what's tertiary and  
what's unclassified. In rural areas I tend to tag roads wide enough  
for cars to pass as tertiary and narrow lanes as unclassified. How  
many houses are needed for the residential tag is obviously a matter  
of judgement as is application of the service tag. I have seen some  
wrongly tagged roads but I would guess nearer 5% than 80%.

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