What is the famous line of latitude
north pole, border or equator

One degree of latitude, called an "arcdegree," has a width of about 69 miles, and the circles of latitude get smaller as they move away from the equator because of the curvature of the earth. There are 90 lines of latitude north of the equator and 90 lines south of it. Other important lines of latitude include the Tropic of Cancer, which is situated 23 degrees, 26 minutes and 21 seconds north, and the Tropic of Capricorn, which lies the exact same distance south of the equator.

a. it led to stricter immigration laws.