The answers are "Equator" and "Prime Meridian"
The grid system gives every point on the earth an address that can be represented as the intersection of two lines, latitude and longitude. The equator is the starting point for measuring latitude (0 degrees latitude), the numbers measure how far north or south of the equator a place is.
Longitude shows how far a location is east of the Prime Meridian (0 degrees longitude) , which runs vertically, north and south, right over the British Royal Observatory in Greenwich England, from the North to the South Pole.
