1.Latitude is imaginary lines that run around the earth parallel to the equator. It is measured from Equator.Hence equator is considered at 00 latitude.
2.Longitude is imaginary lines running from North Pole to South Pole. The lines are farther apart at Equator and get closer and closer as they approach pole. It is measured from prime meridian which runs through Greenwich in England.Therefore prime meridian is considered at 00 longitude.