That's quite detailed. I've tried the concept over a big parking lot and got close to a penny that couldn't be seen unless you were within 10 feet.
Gershon, have you ever played with a mountaineering altimeter like a Thommen Everest? I use one when hiking big elevation changes. A compass bearing to a feature, and a glance at the altimeter puts you right on the map. You have to reset the altimeter at known points on the map once in awhile to account for pressure changes but it's actually quite accurate.