import math def great_circle(lon1, lat1, lon2, lat2): radius = 3956 # miles x = math.pi/180.0 a = (90.0 - lat1)*x b = (90.0 - lat2)*x theta = (lon2 - lon1)*x c = math.acos(math.cos(a)*math.cos(b) + math.sin(a)*math.sin(b)*math.cos(theta)) return radius*c