Drawing with breadcrumbs

Most GPS units have some kind of "breadcrumb" feature that tracks where you've been. Almost as soon as consumer GPSs appeared, creative types began using the breadcrumbing to draw invisible glyphs on the landscape, "painting" with their movements.

Some are crude:



Some are literal:



Some are funny (at least, if you used to play Space Invaders):




More examples:

http://images.google.com/images?q=gps%20drawing

http://www.gpsdrawing.com/
http://www.gpsdrawing.com/gallery.html

http://www.nytimes.com/2009/08/20/fashion/20GPS.html?_r=2&src=twt&twt=nytimes