To construct a perspective view of the armillary sphere with the terrestrial globe and the flat representation of the oikumene, Ptolemy (ca. 100-ca. 175 CE) begins by tracing the largest circle on the sphere, the horizontal diameter, that is, the Equator, and the vertical diameter, called the solsticial colure. The cosmographer then measures an arc of 23°50' and draws it on the circumference, on either side, at the ends of the diameters. With the points obtained, he can trace the main celestial parallel circles: the Arctic polar circle, the Tropic of Cancer, the Tropic of Capricorn, and the Antarctic polar circle. He then divides the radius of the circle into four equal parts and, opening the compass by three units, he traces the circumference of the terrestrial globe. Next, he divides the radius of the globe into 90 parts and marks the latitudes of the main terrestrial parallels on the central meridian: the Syene parallel, the parallel called anti-Meroë, and the Thule parallel. He draws a horizontal line passing through Syene and stretching beyond the edges of the drawing, imagining it as the representation of the axis of the visual pyramid. He then chooses a point situated a short distance below the anti-Meroë parallel and draws a line of sight passing through the intersection between the Equator and the largest circle of the armillary sphere. At the point where this line meets the horizontal line passing through Syene, Ptolemy places the observer's eye. Imagining, now, that the observer would view the model from the side, Ptolemy identifies the central meridian, called the equinoctial colure, as the plane of the drawing seen in profile. He then projects the two nearest and farthest points of the parallel circles, obtaining all the points needed to draw the parallel circles in perspective. Imagining, now, that the observer would view the model again from the front, Ptolemy realizes that every parallel circle will have to pass through four points, two lying on the largest circle of the sphere, and two on the central axis. Geometers would usually construct two arcs passing through three points, drawing the circle foreshortened and with pointed ends, so as to highlight the diameter of the circle even without drawing it. Ptolemy is aware, however, that a foreshortened circle, even though heavily flattened, will always appear as a continuous curve. He therefore advises against using the traditional method. Adopting a geometric construction but without explaining it, the cosmographer draws the parallel circles correctly as ellipses. Since the terrestrial globe is a solid body, the rear portion of the ellipses remains hidden behind the Earth. And since these rings have a certain thickness, Ptolemy recommends that they should be represented by a line of variable thickness, heavier in the front and gradually thinning toward the back. The cosmographer from Alexandria explains that the same rule should apply to the color and shading, which ought to vary with distance. Ptolemy goes on to draw the map of the oikumene (that is, the inhabited world). First, he traces the horizontal line representing the parallel passing through Syene. Next, he draws a line of sight to the point marked 63 and locates a point on the circumference of the terrestrial globe that allows him to draw the arc of the parallel passing through Thule. After applying the same construction method for the point marked 16°30' below the Equator, he draws the arc of the parallel known as anti-Meroë in a similar manner. To trace the meridians, Ptolemy divides the straight line of the Syene parallel and the arcs of the Thule and anti-Meroë parallels into equal parts. He then draws a series of arcs passing through three points. After tracing the other parallels as well, the cosmographer draws the outlines of known lands and writes in the names of places and winds.