Fewer flights to ski destinations

— -- About this graphic:USA TODAY analyzed domestic airline schedule data from OAG — Official Airline Guide for December through March. The data reflect what airlines reported to OAG as of Dec. 8.

We focused on four popular U.S. ski destination airports that most skiers either fly to or where they catch a connecting flight. The graphic shows all non-stop domestic routes to each airport, the average number of daily seats and the percentage change from last year.

We analyzed data for December through March because they are the busiest travel months to ski destinations.

In addition to showing whether existing routes are gaining or losing seats during the upcoming ski season, the graphic also identifies routes that lost all service, as well as routes that gained new service.

We measured seats rather than flights because that takes into account plane size.

Some routes have large percentage increases, which happens when schedule changes begin in the middle of a month. For example, Salina, Kan., to Denver shows a more than 1,000% increase for December through March. That's because the route gained new service in the last days of March 2008, so the number of seats for the December 2007 through March 2008 period is very small.

We will update this interactive graphic throughout the ski season.