I have ask myself for some time now how I could have an estimation of the
completeness of OpenStreetMap when
it comes to ski pistes. I’m certain that with our more than 100’000 km of
pistes, downhill and cross-country combined, we are the biggest global ski
pistes database of this type, but what exactly remains to map? I needed
something to compare to.
There is this great site called Skimap.org where contributors can upload scans and
photos of ski maps from their favorite ski area. They have more than 3000 ski
area listed. These ski areas location are crowd-sourced by their contributors,
and skimap.org offers an open API. So I can certainly find a way to compare
this with OpenStreetMap data, no ? Yes, so I did. And many thanks to
Russel for making Skimap.org !
The comparison goes both ways, first there is a long list called
Pistes missing
from OpenStreetMap.org.
Then we have a map showing Ski areas
missing in Skimaps.org.
It’s not perfect, because there are OSM ways on one side that are not really
(or rarely) grouped as ‘ski resorts’ and single points on the other side. So of
course in some case the distance threshold chosen (5km) is maybe not the best,
and in some case Skimap.org ski area
localization could be improved.
OpenStreetMap ‘ski areas’
No, they are not built-in in the OSM database. There is the tag
‘landuse=wintersports’ to tag ski resorts, but it is seldom used. The rejected
relation proposal ‘site=piste’ attracts even less contributions.
So for this comparison they are build in a database like
this :

The pistes from OSM are buffered by 500m, then glued in big polygons. Very
big polygons (>30km) are split in equal size rectangular chunks ranging from
20km to 40km. This is a bit arbitrary but allows to more or less efficiently
separate interconnected ski areas.
In the end, this gives >3500 downhill ski areas, and the same number of
nordic skiing areas.
What have I found ?
First a really good news : both projects contributors can still have a
lot of fun contributing for a while. Skimaps.org excels in the USA, and OpenStreetMap.org is better in
Europe.
At first glance around 800 ski areas can be found in Skimap.org but not in
OpenStreetMap. For Skimap.org, a lot of small and micro downhill
resorts are missing (apparently > 1500). For nordic skiing, it’s really
worse, but it’s not really the target audience I guess.
Also, OSM seems more complete
when it comes to lifts (aerialways) than for ski pistes themselves. I would
risk an explanation here. There is a lot of gondolas enthusiasts
(https://www.remontees-mecaniques.net/, http://www.funivie.org/web/,
Lift-World.info https://lift-world.info/, ...), and I suspect people are
mapping lifts systematically. Armchair mapping is also possible for aerialways
on the contrary to ski pistes.
How does it helps ?
Both project’s data have open license, but not compatible (CC-BY-SA vs
OdBL). So each can be used for the other as an inspiration, but not as a direct
data source. Needless to say ski maps uploaded at Skimap.org are for the vast
majority copyrighted and not be used for mapping at OSM.
For Skimap.org contributors, they can
use the map produced to spot a ski area in OSM, investigate on the web and find
documentation of interest for the project. For OSM contributors, well, as usual :
find a place with ski pistes to map, take a train ticket, your gear, GPS and
go !
More
Skimap.org also have some more
information about its ski areas, for example if they are closed. This could be
used to spot places in OSM where
some map curating is needed. Also, I spotted on the maps some isolated pistes
in OSM that looks strange. In short, some idea for ski-related QA in OSM.
Copyright notice
OpenStreetMap® is open data, licensed under the Open Data Commons Open
Database License (ODbL) by the OpenStreetMap Foundation (OSMF).
Skimap.org by https://skimap.org/ is licensed under a Creative Commons
Attribution-Noncommercial-Share Alike 3.0 United States License.