A(n) is a line that runs from the north pole to the south pole and connects points of equal longitude.

The Meridian

Explanation:

Its an imaginary line that runs from North to South pole and connects points of equal longitude, basically a line of longitude. Each meridian is perpendicular to all circles of latitude. Each of the same length and thus measuring 20,003.93 kilometers. The term median comes from the Spanish word of Midday. The concept was given by Eratosthenes, this meridian passes through the Greenwich Park, England and was called s the prime meridian set to zero degrees. As it was in the interest of nations to set up a time zone to benefit from fast-growing economic productivity. Unifications of the astronomical, nautical and civil days in one.Similarly, the magnetic median connects the north to south poles and has been taken as a horizontal line. Passing at an angle of 90 degrees from the equator to both the poles.

Themes; subfields is the answer