Earth's surface area = 5.1e14 square meters. Give each of 5.1e12 same-sized patches an integer identifier (one way or another): that's 8.3 base-34 digits (disal

Earth's surface area = 5.1e14 square meters. Give each of 5.1e12 same-sized patches an integer identifier (one way or another): that's 8.3 base-34 digits (disallowing 'I' and 'O'). If you detect all single-character substitution errors, that rounds up to 10 characters -- oh, well. (This kind of scheme would get you better worst-case resolution with your 10 characters. I'm not sure what it is for the posted code.)