His suggestion that eclipses of the moon could be used to determine the longitude of places was an important idea which was relevant to his other major contribution, namely cartography.
Ang kanyang mga mungkahi na eclipses ng buwan ay maaaring gamitin upang matukoy ang longitude ng mga lugar ay isang mahalagang ideya na kung saan ay may kaugnayan sa kanyang iba pang mga pangunahing kontribusyon, namely kartograpya.