Lines of longitude measure distance from where, the equator or the prime meridian?

These lines measure the distance of Prime Meridan

Prime Meridian line divides the earth into two hemispheres as South hemisphere and North hemisphere. Lines of longitudes runs vertically on the globe as up to down to connect these north-south poles. These lines are used to measure the distance of East or West location from the prime meridian. These lines cross the equator at the right angle () also known as Greenwich Meridian.

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