Before revision: The individual rectangles that make up the system each measure 1 degree of longitude by 0.5 degrees of latitude and are intended to be roughly square in real world use (approximately 30 nautical miles by 30 nautical miles at 60°N) although the actual width varies with latitude .
After revision: , gradually becoming wider than they are high south of 60°N, and higher than they are wide further northThe individual rectangles that make up the system each measure 1 degree of longitude by 0.5 degrees of latitude and are intended to be roughly square in real world use (approximately 30 nautical miles by 30 nautical miles at 60°N) although the actual width varies with latitude .