Ski It If You Can

Finding the most difficult skiing in North America

by Seth Brown

Trail Composition

In North America, on piste alpine skiing is classified by a rating system where trails are graded by difficulty. Novice, intermediate, and expert trails are denoted by a green square, a blue circle, and a black diamond, respectively. Each mountain has a specific composition of green, blue, and black trails. For example, Stowe Mountain is composed of 16% , 59% , and 25% .

Ski Difficulty

In the ternary diagram below, the trail composition of 2028 ski mountains across North America are depicted using a barycentric coordinate system. The number of mountains in each hexagonal bin is encoded by color intensity and the predominant trail difficulty is represented by color hue. For example, a light blue bin indicates that there are only a few mountains in the bin and that the predominate trail composition of the bin is intermediate. Hovering over a bin with the mouse reveals the individual mountains comprising the bin.

Extreme Outliers

Most mountains are found at the approximate centroid of the ternary diagram. The mountains with the most difficult terrain are located in the extreme lower right corner. At this position, a lone bin slice contains two mountains. The mountains in this bin are composed of almost all expert trails and the terrain diffculty at these resorts deviates substantially from all other mountains in North America. These two outliers are Silverton Mountain located in Colorado and Mount Bohemia located in Michigan.

Elevation Change

Silverton and Mount Bohemia are both composed of dificult terrain; however, they differ greatly in elevation change. With all other things being equal, a mountain with longer runs is more difficult. The small multiple below illustrates elevation change from resort base to peak of five different representative mountains including Silverton and Bohemia. The extent of elevation change in North America is bounded by Mulligan's Hollow in Michigan at only 130 feet and Revelstoke Mountain in British Columbia at almost a mile of vertical elevation change.

To compact the dynamic range, the vertical axis encodes the square root of elevation change while the area of each bubble chart denotes the number of trails at each resort. Each inner node depicts one trail and the color represents trail difficulty. The number of inner nodes cooresponds to the number of trails at a resort.

Silverton Mountain

Colorado's Silverton Mountain has the most difficult ski terrain in North America. The ternary plot illustrates its extreme difficulty while the small mulitple highlights its large vertical elevation change. Silverton is the only mountain with 100% expert terrain and it has over 3 orders of magnitude more elevation change than the next most difficulty resort—Mount Bohemia. Together, these features make Silverton the most difficult ski resort in North America. Ski it if you can!


Additional details about the design and implemenation of this project can be found in this blog post.