[Tagging] maxspeed:type vs source:maxspeed

[Tobias Zwick]

> [...] there are already 2 different schemas to fill the same thing,
> why create a 3rd ? wouldn't it be more reasonable to use
> maxspeed:type=default or =unsigned or =nosign for example ?

Also a possibility. I used maxspeed:signed only in the example to make
my point about separating the information. Other possibilities include
maxspeed=implicit, maxspeed=default, maxspeed:default=yes/no.

I have come to accept that there are good reasons why it is difficult to
make progress on this topic:

1. default max speeds are a complicated topic

2. (thus) it is very difficult and requires thorough research to find a
   scheme that is applicable for the whole world and future-proof

3. due to the complexity of inferring maxspeeds, it is very
   inconvenient for data consumers (including QA tools) if no explicit
   maxspeed-value is set

  a) source:maxspeed is still quite simple to use because a 1:1
     mapping is possible, e.g. source:maxspeed=DE:urban -> maxspeed=50
     In other words, it's a good start for getting away from explicitly
     tagged speed limits and is a product of the circumstances

  b) as long as the meta-information for each country necessary to
     infer default speed limits is not freely and easily available
     somewhere in a structured form, data users will likely be very slow
     to adopt a more complex scheme that is applicable worldwide.

I think as maxspeed:type was not able to replace source:maxspeed, so
will any other new scheme as long as it is not applicable to any country.

I started https://wiki.openstreetmap.org/wiki/Default_speed_limits
because of Point 2. Point 3.b) is the reason why I want that table to be
machine-readable and why I also plan to implement a parser for that page
as well as (maybe) a library that implements the rules as given in the
"how to read this table" section.

On 19/09/2018 23:35, marc marc wrote:
> Le 19. 09. 18 à 22:33, Tobias Zwick a écrit :
>> separate the information stored in "source:maxspeed":
>> --------------------------------------------
>>
>> 1. Information about whether there is a sign or not (=whether a
>>     default speed applies or not)
>>
>>       highway=motorway + maxspeed:signed=no
> 
> I agree with this but there are already 2 different schemas to fill the 
> same thing, why create a 3rd ? wouldn't it be more reasonable to use 
> maxspeed:type=default or =unsigned or =nosign for example ?
> 
>> 3. removes superfluous country ISO-code
> 
> I agree with this point, any preprocessor is able to known that every 
> maxspeed limite in a country is related to the default value of this 
> country.
> 
> that being said, the whole discussion has nothing left with the initial 
> topic: is it not so much to migrate source:maxspeed into maxspeed:type 
> since source:maxspeed is not the source as in the osm sense but the type 
> of panel (or its absence) having effect on the way concerned.
> if it is already so difficult to make progress on this point, I find it 
> difficult to imagine that an even more important change could lead to 
> something other than an additional new scheme and therefore an even 
> greater fragmentation is even more duplicated information
> 
> Regards,
> Marc
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