[talk-au] Aus tagging guidelines on highway surface tags

[cleary]

I agree that road surface tags are important, especially in rural and isolated areas in Australia.



On Sun, 31 Jan 2021, at 3:13 PM, Little Maps wrote:
> Hi folks, wondering if I can promote some discussion about the section 
> of the Aus tagging guidelines on adding surface tags on roads. The text 
> currently reads,
> 
> “For most types of highway=* tags you don't need to specify the 
> surface=paved key/value pair as this is assumed, however make sure you 
> tag the road surface when it isn't a paved road.”
> 
> This assumption is fine in large cities but is problematic in rural and 
> regional Australia. Can I suggest that it is replaced by something like 
> the following...
> 
> "Surface tags should be added to roads wherever possible, especially in 
> regional areas. This advice differs from that on the international 
> key:surface wiki page, which states that, 'there is normally an 
> assumption that the surface is surface=paved unless otherwise stated.' 
> However this assumption is not valid across regional Australia as: (1) 
> most roads, including many major roads, are unpaved, and (2) mapping 
> intensity varies greatly among regions. Many roads that do not have a 
> surface tag may not have been examined by mappers. Adding a surface tag 
> will assist data users and help mappers to further refine the regional 
> road network."
> 
> Long rationale (not for posting on the oz tagging guidelines page)...
> 
> Surface tags have been added to relatively few rural roads in many 
> regions. Hence, the most prudent assumption is that the absence of a 
> surface tag means that the road surface has not received attention from 
> mappers. A default assumption that any road without a surface tag is 
> actually paved is most likely wrong.
> 
> Efficiency of mapping. Even if one has no interest in adding tags to 
> paved roads, the most efficient way to refine surface tags is to 
> interrogate untagged roads and tag them (e.g. by using an overpass 
> query that distinguishes untagged, paved and unpaved roads, and 
> variants thereof. Untagged roads can be inspected and tagged as 
> appropriate.) However, if mappers are advised to not tag paved roads, 
> then every paved road that is untagged needs to be re-examined each 
> time this is attempted. This wastes a lot of effort.
> 
> Some apps — especially routing and cycling apps (e.g. Osmand and 
> Komoot) — allow users to request paved or unpaved routes. Regardless of 
> the (unknown) assumptions that routers make about road surfaces when 
> creating routes, apps like Osmand present the data back to users. The 
> suggested route may be X% paved, Y% unpaved and Z% unknown. In many 
> regions, Unknown is the largest category. This doesn’t inspire 
> confidence in the route or underlying data.
> 
> Some assumptions about road surfaces can obviously be made. For 
> example, a primary road is more likely to be paved than an unclassified 
> road. However, most roads in rural areas are tertiary or unclassified. 
> Some are paved, many not; the ratio varies unpredictably across regions 
> and it is impossible to predict which roads are paved unless they are 
> tagged.
> 
> Perhaps not surprisingly, the OSM wiki on key:surface gives conflicting 
> advice, beginning with the (European?) position that “there is normally 
> an assumption that the surface is surface=paved unless otherwise 
> stated” and later adding an (American?) view that, “There are no 
> default values for surface, it is generally considered as OK and 
> desirable to tag it explicitly for all roads.” The latter approach 
> seems most appropriate in regional Australia.
> 
> Adding surface tags to both paved and unpaved ways is the most 
> efficient method to: (1) allow data users to accurately predict road 
> conditions (this benefits users) and (2) improve the rate at which 
> unpaved roads can be reliably distinguished from paved roads (this 
> helps future mappers). They may be redundant on motorways, trunk and 
> primary roads, but these make up a tiny proportion of roads in regional 
> Australia and can all be coded with a minimum of effort.
> 
> Advising mappers to not add a meaningful tag would appear to be counter 
> to the goals of accurate tagging. Can we change our advice to encourage 
> mappers to add a surface tag wherever possible?
> 
> Thanks for your time, I'm keen to hear your thoughts. Best wishes, Ian
> 
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