First, they went into groups, each with two sheets of blank 8.5x11. On each page, they were told to place two dots randomly (next year, maybe only one dot). From there, they were to draw concentric rough circles. A few students picked up that they looked like topographical maps -- sure enough, when I had them count from 0 going up by 500ft (yes, feet) they quickly agreed they were topo maps. I then quickly dropped the maps into my scanner at home and posted the JPGs to our Ning. From the digital copy, each student planned their own ski run, taking into account whether they were looking for something easy or hard. I'm not a skier but there was lots of discussion of diamonds and circles and green and black.
They then worked on analyzing their runs... what's the slope of each section? What's the total length of the run (thank you Pythagorean Theorem). They also transferred the data to GeoGebra to get a 2D representation of the run (where they started last year).
And what prompted me to move to 3D? Google SketchUp! The Jpeg of the topo map can be imported into SketchUp and set as the base. Then, using the contours tool, the contours can be traced and then "lifted" to form a three dimensional representation of their mountain (I got a "Dude...." when I showed that to the class. "Dude indeed" I responded).
A good time was had by all... and a lot of nice discussion of slope and length of segments.