The fourth section would consist of Arabia Felix, the Arabian Gulf, and the whole of Egypt and Ethiopia. Its length bounded by two meridians, one drawn through its most western point, the other through its most eastern; and its breadth by two parallels through its most northern and southern points. For this is the best way to describe the extent of irregular figures, whose length and breadth cannot be determined by their sides.

In general it is to be observed, that length and breadth are to be understood in different ways, according as you speak of the whole or a part. Of a whole, the greater distance is called its length, and the lesser its breadth; of a part, that is to be considered the length which is parallel to the length of the whole, without any regard whether it, or that which is left for the breadth, be the greater distance. The length of the whole habitable earth is measured from east to west by a line drawn parallel to the equator, and its breadth from north to south in the direction of the meridian; consequently, the length of any of the parts ought to be portions of a line drawn parallel to the length of the whole, and their breadth to the breadth of the whole. For, in the first place, by this means the size of the whole habitable earth will be best described; and secondly, the disposition and configuration of its parts, and the manner in which one may be said to be greater or less than another, will be made manifest by thus comparing them.