In De situ orbis, Mela divided the earth into five regions which were habitable. It is apparent that some of his knowledge was derived from earlier writers, most notably, the Greek geographer Eratosthenes. His knowlege of western and northern Europe was superior to that of the earlier Greek writers, having benefitted from the Roman conquest and occupation of much of Europe. His descriptive method was to follow the coasts of oceans and seas, no doubt relying on accounts from sailors. The inaccuracies of his descriptions are, at least in part, attributable to the inability of the ancients to effectively determine latitude and longitude.