Umbra is a exploration application based on the the Fog Of War concept used in strategy games. On the map the unexplored area is displayed grayed out while the explored part is clear. The application needs a GPS fix in order to mark an area as explored as the accuracy from the other location sources is not good enough. Currently the minimum accuracy needed for saving the explored area is set at 100 m (600 feet). The accuracy is displayed as a disc around the current position. Umbra saves your exploration in an internal database (nothing is sent over the network).
http://earth.google.com/outreach/images/ft_heatmap.png
Add a heatmap with colour depending on the number of passes through an area.