Visualizing Velocity Along a Path on a Map

This map shows trip data from my GPS logger using a spline which gets thicker when I spend more time in a place (like the mall or a coffee shop). You'll have to use your mouse wheel to zoom, for now.

Once I was able to draw splines with varying thickness I couldn't resist plotting some GPS data on a map. One sleepless night later, I completed this demo which shows me running some errands a few weeks ago. The spline gets thicker when I stop at a restaurant, a gas station, a Salvation Army clothes donation bin, and even at traffic lights. There's also an interesting intestine-looking shape if you zoom in on Metropolis mall on the east side of the map.

At this point, sleep depro euphoria is definitely kicking in, but I'm super excited about the possibilities with this! If you plotted data from a hike it would show you where the going was rough and you had to slow down and/or take lots of rests. I also wonder what skiing looks like, or taking a bus.

Any ideas for useful applications?