Ptolemy's maps of Earth and the heavens: a new interpretation
The author has carefully analyzed Ptolemy's two treatises, The Geography and The Planispherium, concerning the mapping of the points on a sphere into the plane. The commonly accepted interpretation was that Ptolemy utilized the mathematical tradition of the stereographic projection in both works although his geometrical procedures were not very elegant and consistent. After comparing the four maps, three in The Geography and one in The Planisperium, the author offers a new interpretation: Ptolemy's concern was not so much in mathematical consistency as in visual verisimilitude. Just as Ptolemy in The Geography simply offered the procedures for drawing maps in three different ways which are not stereographic, so in The Planispherium he just intended to draw the celestial circles in the plane without being involved in pointwise stereographic projection. Thus the instrument described in this treatise was different from the later astrolabe. This is a very interesting and stimulating paper on the history of stereographic projection as well as that of the earliest stage of `astrolabe'.
scientific article; zbMATH DE number 148362