We do not know whether [Hipparchus] drew maps--perhaps he did--but the truth is that in his day he could not possibly have applied his projections to the globe because the necessary data, in the form of correct findings of latitudes and longitudes of a very large number of places over the known areas of the earth, were not available. This was the weakness of all Greek cartographic science. In Greek times mathematics was in advance of mechanical instrumentation: There was no instrument for easily and correctly determining the longitude of places. However, the Piri Re'is and the other maps we went on to study, seemed to suggest that such an instrument or instruments had once existed, and had been used by people who knew very closely the correct size of the earth. Moreover, it looks as if this people had visited most of the earth. They seem to have been quite well acquainted with the Americas, and to have mapped the coasts of Antarctica.
Charles H. Hapgood Maps of the Ancient Sea Kings: Evidence of Advanced Civilization in the Ice Age