[Tagging] importance=* tag (for transportation etc)

Alexander Matheisen AlexanderMatheisen at ish.de
Sun Mar 20 00:12:10 UTC 2016

Am Samstag, den 19.03.2016, 02:13 +0100 schrieb Martin Koppenhoefer:
> sent from a phone
> > Am 18.03.2016 um 22:36 schrieb John Willis <johnw at mac.com>:
> > 
> > OSM wants local knowledge, per this idea, but not the kind that
> > could lead to better rendered maps or better routing. 
> importance is relative and it depends on your criteria which things
> you consider more important than others. I agree that we should
> better map the properties that make something important rather than
> stuff it all in a generalized "importance" tag. For mountains this
> will likely mean to look at prominence and topographic isolation, for
> train stations it can be amount of passengers or trains per time, or
> size (amount of platforms), availability of highspeed trains, etc.,
> for airports similarly you could look at amount and size of runway/s,
> passengers/time, amount of connections etc.
> the problem with rendering is that these calculations are typically
> too expensive to do them on the fly, but we could use precomputed
> data and integrate it in a coastline like way (external shape file or
> pre-computed attribute)

If you have a look at the highway=* tagging: This scheme is subjective,
but there is no alternative. Without such categorization by mappers, it
would be necessary to calculate the type of road just by absolute
values such as the width, the surface, the number of cars per hour, the
number of lanes, etc. Everybody should agree that that would not work.

As the person who created that station importance draft, I will focus
on stations, but for other features like mountain peaks the situation
should be similar: It is not possible to calculate the importance of a
station just by some values. Values like the number of platforms or
passengers are just absolute values, but the importance of a station is
a relative information which is influenced by neighbouring features.
Without any importance-tag, it would be necessary to analyse many other
feature, which is very difficult. The importance of a station is
influenced by so many aspects that it is nearly impossible to calculate
it, especially in a reasonable time.

I also see problems in getting some of the proposed values. For
example, the amount of passengers or trains per time is difficult to
measure for a mapper and is not easy to be checked by other mappers. I
do not see a possibility to map such values for a larger number of

I also see the problem that calculating the importance by a complex
algorithm might be very intransparent. There will be situations where
such algorithms produce results that does not fit to reality, but
mappers will not have any possibility to influence the results.
Currently one strength of OSM, compared to many commercial services, is
that we use the local knowledge of the mappers. With subjective tags
like highway=* they can map information that helps applications to
produce the best results.

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