Convert from square chain [Gunter, survey] to square gigameter

Unit Definition (square chain [Gunter, survey])
The square chain [Gunter, survey] is a traditional unit of area in English surveying, defined to be the area of a square whose side equals Gunter's chain (4 rods or 22 yards). Thus the square chain equals 16 square rods, 484 square yards, 4356 square feet, or exactly 0.1 acre.

Unit Definition (square gigameter)