The web based project Cabspotting traces San Francisco's taxi cabs as they travel throughout the Bay Area. The patterns traced by each cab create a living and always-changing map of city life. This map hints at economic, social, and cultural trends that are otherwise invisible. The Exploratorium has invited artists and researchers to use this information to reveal these "Invisible Dynamics."
They must have a great collection of GPS tracks as the project was launched in 2006. So is could be two and something years worth of tracking data. There are also some nice animation on their website. Some artists where invited to use the data for their work some of these examples are here. Two example movies from their visualisations.