Draw a cube in perspective very accurately. Subdivide each face. Using the center subdividing lines of each face, emphasize the three square planes which intersect the interior of the cube. (figure 1)
As described above, construct a circle onto each of these squares. Construct patiently and accurately. You should have one horizontal circle, or latitude line corresponding with the equator, and two vertical, or longitudinal circles. (figure 2)
At this time draw a true two-dimensional circle which touches the outer edges of each ellipse. Imagine drawing it on the page with a large circle template. To add additional latitude lines, the procedure is the same as with the cone. Begin by marking a point anywhere on the center axis line. Using the vanishing points as guides, project lines through this point which cross the vertical longitude circles. If your sphere has been accurately constructed this will give you four additional points at which to construct an additional latitude line. (figure 3)
Repeat to construct additional latitude lines.