To draw the map of the oikumene (that is, the inhabited world) with the second cartographic method, Ptolemy (ca. 100-ca. 175 CE) begins by setting the boundaries of the area to be drawn, tracing a rectangle whose width is equal to twice its height. The shorter side is divided into 90 parts corresponding to the degrees of one-quarter of the Earth's meridian. Starting from the bottom, he then plots on the central axis the points corresponding to the parallels passing through anti-Meroë, the Equator, Syene, and Thule. Next, he traces a horizontal line passing through the point corresponding to Syene. The line obtained represents the image of the oblique circle of the ecliptic as it appears to the viewer. The ecliptic looks like a straight line because it lies on a plane that is level with the observer's eye. The segment connecting the equatorial point and the end of the horizontal line is the chord of the arc that, in this rendering, denotes the circle of the Equator. The perpendicular drawn from the center of the chord marks the center of curvature of the equatorial arc on the central axis. Having found the center of this arc, Ptolemy then draws the concentric arcs representing the parallels passing through Thule, Syene, and anti-Meroë. Taking five units as the measurement of the interval between meridians on the Equator, Ptolemy divides the equatorial arc into 36 equal parts, in other words, 180 units. By means of a mathematical calculation or, using the more practical solution of a terrestrial globe, he then measures the value of the same intervals on the Thule, Syene, and anti-Meroë parallels. To draw the meridians, he constructs a series of arcs passing through three points chosen on the Thule, Syene, and anti-Meroë parallels. The outermost meridians have a radius of curvature easily measured with a compass. By contrast, the innermost meridians approaching the straight line have a very large radius, which the cartographer was obliged to measure with a string. Unlike the parallels, which are concentric arcs, the meridians are arcs whose curvature increases from the center outward. The central meridian, which lies on the plane level with the observer's eye, appears to be a straight line. Ptolemy interrupts his explanation of the cartographic method at this point, but the tables illustrating the fifteenth-century manuscripts of the Geography clearly show that the next step consisted in drawing the parallels every 5° of latitude or at variable latitudes. This was the method used to fill out the cartographic grid that served as a guide for drawing coastlines, cities, mountain ranges, rivers, and lakes. Colors, inscriptions, depictions of winds, and ornamental motifs completed the pictorial and cartographic representation of the map of the oikumene.