Yesterday I made what I believe may be one of the world's largest Valentine's Day cards.
Measuring nearly ten square miles, it consists of precisely marked coordinates which, if traced on a map, spell out "I ♥ U".
I got the idea right after I acquired a GPS the other day -- a gizmo I have no actual use for, but instead got merely because they're nifty. The first step was determining points; I used a Rutgers bus map and a magic marker to draw the I ♥ U message, one character per campus. Then I chose a minimum number of points which, when traced between, would be recognizable. This was easy for "I" and "U", a bit harder for the heart -- especially given the limitations imposed by the terrain itself. A point couldn't be in a building, or on private property, etc.
I spent the rest of the day on foot with the GPS and a fat permanent marker. At each point, I drew on the ground (mostly concrete sidewalks) a heart, the latitude and longitude (WGS 84 datum), and the distance and magnetic bearing to the next and previous points.
I then gave the list of coordinates to my girlfriend. (I could have just given her the first point, but that'd be too much work... and it is Valentine's Day...)