[Tagging] maxspeed:type vs source:maxspeed // StreetComplete

Tobias Zwick osm at westnordost.de
Wed Sep 19 20:33:23 UTC 2018

>> Anyway, for a beginner : is one key even better ? -> should we allow
>> “maxspeed=no_sign” ? Or/and “maxspeed=default” ?
> Way too ambiguous to be remotely workable in North America.

Is it? I think what djakk is arguing for, and me as well, is to separate
the information stored in "source:maxspeed":

1. Information about whether there is a sign or not (=whether a
   default speed applies or not)

2. Auxiliary information, if necessary, to automatically infer the
   speed limit from the given OSM tags.

Examples for when no maxspeed sign is in sight:

1. Motorway in France (FR):
     highway=motorway + source:maxspeed=FR:motorway
     highway=motorway + maxspeed:signed=no

2. US interstate in Montana (US-MT):
     highway=motorway + source:maxspeed=US-MT:interstate
     highway=motorway + maxspeed:signed=no + ref~^I
   (maybe ref-starts-with-"I" is not necessary because all interstates
    are tagged as motorways?)

3. Road without asphalt or concrete surface in Quebec (CA-QC):
     maxspeed:signed=no + surface!~asphalt|concrete

4. Road with 4 lanes in Delaware (US-DE):
     maxspeed:signed=no + lanes=4

5. Urban road in Germany (DE):
     maxspeed:signed=no + urban=yes

etc., you get the idea(?)
The tags are just examples.

What are the advantages?

1. separating information about the legal road type from whether
   there is a sign or not

   a) makes it easier for contributors to supply the latter as they do
      not have to know precisely about the current speed limit
      legislation. Good for verifiability.
      (maxspeed:signed=no --- source:maxspeed=XX:a_legal_category)

   b) that legal road type (like whether a road is within a
      built-up area or not) is also an important information, even when
      an explicit speed limit IS signed. For example to determine
      the max allowed speed for other vehicle types such as trucks or
      whether a particular vehicle category is allowed on that kind of
      (a_legal_category=yes ---- source:maxspeed=XX:a_legal_category)

2. using existent tags (e.g. surface, lanes,...)

   a) removes duplicated information
      (lanes=4 --- source:maxspeed=XX:4_laned)

   b) tries to avoid as much as possible "legal road type" categories,
      as these, like default speed limits, may change anytime and have
      problems with on-the-ground verifiability. Thus: better future-
      (source:maxspeed=AT:living_street does actually not exist anymore
       since legislation change in 2002)

3. removes superfluous country ISO-code. Country boundaries information
   is already available in the OSM database, data users can just use a
   (reverse) geocoder to find where a street is.
   (I wrote Java library recently that does this offline in ~0.1ms)

(Ask me for concrete examples)

On 19/09/2018 17:44, Paul Johnson wrote:
> On Wed, Sep 19, 2018, 10:22 djakk djakk <djakk.djakk at gmail.com
> <mailto:djakk.djakk at gmail.com>> wrote:
>     Yes Paul, I should not forget the beginners ... 
>     I am not a beginner anymore but I still found “source:maxspeed=“ for
>     roads a little confusing, as we should use “source=“ only (?) on the
>     metadata (on the changeset). 
> Specific keys that don't change often and have verifiable source can
> also have source keys, this would be a good example of that being
> appropriate. 
>     Anyway, for a beginner : is one key even better ? -> should we allow
>     “maxspeed=no_sign” ? Or/and “maxspeed=default” ?
> Way too ambiguous to be remotely workable in North America.
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