Ptolemy places Naga Island in the northern part of the Taprobane, and calls it Nagadiboi. He fixes the Galiboi, Moudoutoi, Anouro-grammoi the Soanoi in this region of the Nagadvipa, Describing the whole of the tribes and their settlements, he finds the Sennoi below the Nagadiboi and still below the Sando-kandai. Towards the west of them, and below them are the feeding grounds of the elephants known as the Bouma-sanoi and the Tarakhoi. He fixes them in the eastern part of the Taprobane. Here he finds the Bokanoi, Diordouloi, Rhogandanoi and the Nageiroi.

He identifies the Nagadiba town at 129⁰ 8⁰30’, and Alaba at 131⁰ 4⁰ S.

Ptolemy was then living in Alexandria and this is very close to the Nagadiboi region. Sri Lankan government sees Taprobane as Ceylon and this is incorrect. Ceylon stands for Kolhana and Taprobane identifies the ‘garden of meditation’ means the ‘Tapo-bana’ .

At Alaba Alexander met Darius from where he fled to Oxus; the best identification of the Nagadiboi is found with the Sennoi people who were then living as their neighbour. Sennoi refers to Senani and Sennanigrama of Pali texts. While Senani refers to the shepherd leader of this community then living on the banks of the river Soana( mouth at 122⁰20’ 6⁰15’ and sources at 124⁰30’ and 3⁰), Senani-grama refers to the name of Senani’s settlement. The royal House of Magadha in Buddha’s time belonged to the Senanin shepherdic groups. Senanigrama exactly identifies the place of Buddha’s enlightenment. Senani’s daughter gave the rice milk to the Buddha after his enlightenment.  Story of Naga Muchukunda is well connected like Senani’s daughter Sujata with the story of Buddha’s Enlightenment. Here Ptolemy sees flowing of the river Phasi( mouth at 127⁰ 11⁰20’ and sources at 126⁰ 8⁰). River Ganges has been shown by Ptolemy as a river of the Nagadiboi region.

Story of Galiboi is the story of the epic the Gilgamesh; it identifies the hermitage of Sage Gallaba and it is also well connected with this region of the Taprobane where one thousand Arahats were staying with one name ‘Sundara’. And this identifies the place Sando-kandai near Alsanda or the Alexandria of history. Name of Alexander which is a combination of two names : Alika and Sundara, receives from the sacredness of the two places of this Nagadiboi region.