The chart below shows the five largest ski areas on each continent (except
Antarctica). Africa only has three entries because those are the only ski areas
I found with annotated ski lifts and slopes. Everything is calculated
according to some reasonable yet arbitrary
heuristics so please take the rankings with a grain of salt. If you click
on a ski area, it will be displayed in the map
below.

The Map

All the ski areas in the chart above are annotated on the map below. Clicking
on an area above centers the map below.

How it’s made

Each ski area is defined by something like an alpha
shape, calculated over all the
lifts and slopes. Each “alpha shape” -like area is calculated by first creating
a Delaunay triangulation of all ski lift and slope waypoints. Every triangle
which has a side greater than 1km is then removed. The result is a set of
disconnected shapes all composed of multiple triangles. Each aggregation of
triangles is what I consider a ski area.

In some cases, this can lead to two ski resorts being connected even though you
might have to walk up to 1km to get from one lift to another (e.g. Kitzbühel /
SkiWelt above). In the opposite case (e.g. Oukaimeden), a long lift may not
be counted simply because the points defining it create degenerate triangles.
Nevertheless, in most cases the shapes created reflect the ski areas they
represent quite well.

Here’s the recipe to re-create the graphic:

Download OpenStreetMap dumps of each continent

Filter for lifts and slopes

Sample points along long segments to make sure they’re not split

Calculate a Delaunay triangulation of all the OSM nodes and the sampled points

Exclude all triangles which have an edge longer than 1km (concave hull of sorts)

Polygonize

Google the towns near the resorts to figure out what the resorts are called

Convert to topojson and downsample to reduce the size

Make table using d3.js

Create zoomable map using leaflet.js and a d3.js overlay