What is the standard length of one international nautical mile (NM), and why is nautical distance measured along the latitude scale rather than the longitude scale on a Mercator chart?

1. 1,852 meters; one nautical mile equals one minute of latitude, which remains constant in physical distance, whereas longitude minutes shrink toward the poles
2. 1,609 meters; one nautical mile equals one minute of longitude along the equator only
3. 2,000 meters; Mercator distortion requires expanding latitude and longitude scales at an identical rate
4. 1,852 meters; longitude minutes represent true physical distance while latitude scale is heavily compressed