[OSM-dev] Modeling OSM sidewalk data

Andy Townsend ajt1047 at gmail.com
Tue Jul 12 10:44:03 UTC 2016


On 12/07/2016 08:42, Paul Norman wrote:
> Does anyone have experience consuming OSM sidewalk data and have 
> thoughts about what would be better to work with? 

Rather than having sidewalk data available in a column, I instead with a 
different highway value for "this road has a usable sidewalk".  We 
already have a plethora of highway values, so the extra work to support 
isn't high, and has the advantage that you don't need to mess about with 
the schema (though you do need to reload the database) if anything changes:

https://github.com/SomeoneElseOSM/SomeoneElse-style/blob/master/style.lua#L258

My initial goal was to be able to render sidewalks on unclassified and 
tertiary roads.  Note that there are more values in that list than 
you're probably expecting - that was what was found to be in the data 
when I looked locally.  Here's a diary entry, with a picture of what 
things look like

http://www.openstreetmap.org/user/SomeoneElse/diary/38136

(though I've tidied up the rendering a bit since then).

To address Komяpa's point, it's absolutely true that mapping sidewalks 
as separate ways is something that you need to consider in some cases 
(though I'd dispute that it is "only applicable to cities with a blocky 
structure" - sidewalk=both et al mostly work well in the UK).  In some 
places (e.g. in my experience Helsinki) sidewalks meander off on their 
own and then rejoin roads, and separate mapping makes sense.  Also, if 
you're mapping dropped kerbs etc. for wheelchair use then it's a lot 
easier to map sidewalks separately.

Unfortunately, the biggest problem with "sidewalks mapped as separate 
ways" is that they sometimes tend not to be done very well - often the 
mappers produce something that looks nice on a printed map but doesn't 
represent the topology (by no means always, but often enough to be an 
issue).  For example (not far from Komяpa's link) I very much doubt that 
this shows a correct foot route between the highlighted places:

https://www.openstreetmap.org/directions?engine=graphhopper_foot&route=53.94458%2C27.72384%3B53.94459%2C27.72419#map=19/53.94428/27.72472

The road that these are the sidewalks of 
https://www.openstreetmap.org/way/281594594 has no sidewalk information 
(though in this case, being a living_street, you should be safe walking 
along the middle of the road).

 From the readme of https://github.com/ClearTables/ClearTables it sounds 
like you're trying to process OSM data as it actually exists, not "as it 
ought to be tagged", which means you might have to do something "clever" 
to detect poorly mapped examples like the one above, perhaps based on 
proximity.  I'd be interested to see what you come up with...

Best Regards,

Andy





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