If you stop and think about it, using a rope and a board is much faster than walking a few feet, looking at your GPS, shifting a half step back, checking again, then stomp, then move in the direction you think you need to go, then realize, oops, a step to far that way, better upright that area of crops... oh crap, lost a satellite, now my fix is only good within 3 feet....

A board and a rope is way simpler and faster, at least for certain abstract geometric designs...

Now, if you wanted to make a specific picture, then a GPS could help you, I suppose.

CJSF

__________________
Two years ago moved from my town
I was looking up past the city lights
But the city lights got in my way

See the constellation ride across the sky
No cigar, no lady on his arm
Just a guy made of dots and lines

-from "See The Constellation"
by They Might Be Giants