Geographical Information and Map Making — Geography STD 11 Arts — Question

The principal longitude is called the zero or Greenwich longitude, which indicates the distance of any place east or west of this principal longitude.

Longitudes are semicircles, numbered $180^\circ$ in the east and $180^\circ$ in the west, making a total of $360^\circ.$

Longitudes are parallel to the main longitudes which are semicircles of uniform size.