The first of Ptolemy's writings, Almagest, Arabic for "The Greatest," is the synthesis of his scientific theories about the universe, where a spherical earth resided in the center of a spherical heaven.
The book that earned Ptolemy the distinction as one of the giants in European geographic thought is the Geographia (also known by the name Cosmographia).
In addition to the Geographia and the Almagest, Ptolemy wrote important texts in astrology (Tetrabiblos), biography (a listing of Assyrian, Persian, Greek, and Roman kings), music, optics, and a work titled Planisphaerium, which describes placing a sphere on a flat surface. The original Greek text of the latter is lost, but is known from an Arabic translation made in about A.D. 900 by an unknown translator. Three manuscripts, two of which are nearly identical, survive. The third is a different version, with diagrams (Kunitzsch 1994, 5). The difference in manuscript texts is an example of the challenges of research on the writings of Ptolemy. How close are the surviving manuscripts to the original that was written by Ptolemy? This may remain unknown, but close analysis and comparison of surviving texts might reveal which manuscripts are the earliest and most authentic. In most cases the sources that Ptolemy used in his writings are known, though again, some of these no longer survive.
Ptolemy’s writings "disappeared" from the view of European scholars for centuries. Questions about the surviving manuscripts of both maps and texts of the Geographia are important ones, especially in relation to the transition of the content from handwritten to printed form. Were copies of the Geographia available in Europe during the centuries between its composition and its translation into Latin early in the fifteenth century and its wide dispersal through printing, beginning in the fifteenth century? It seems probable that at least a few Greek manuscripts of the text remained in Europe. Since Greek was not studied in western Europe, however, the Geographia may simply have remained hidden from scholars, who did not have the language skills to use it.