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 :

osm_skimap.png

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.