Portolan Maps

". . . The lines do not resemble the modern map's lines of latitude and longitude that are spaced at equal intervals and cross to form "grids" of different kinds. Instead, some of the lines, at least, on these old maps seem to radiate from centers on the map, like spokes from a wheel. These centers seem to reproduce the pattern of the mariner's compass, and some of them are decorated like compasses. The radiating "spokes" are spaced exactly like the points of the compass, there being sixteen lines in some cases, and thirty-two in others.

Since the mariner's compass first came into use in Europe about the time that these charts were introduced, most scholars have concluded that the charts' design must have been intended to help medieval sailors sail by the compass. There is no doubt that medieval navigators did use the charts to help them find compass courses, for the method is described in a treatise written at the time. . . ".

Note 4: Blundeville's Directions for Constructing the Portolan Design':'

"Of the Mariners Carde and of the marking thereof."

"First drawe with a pair of compasses a secrete circle which may be put out, so great as you shall think meet for your carde, which circle shall signific the Horizon, then divide that circle into foure equall quarters, by drawing two Diameters crossing one anotber, in the center of the foresaide circle with rigbt angles, whereof the perpendicular line is the line of North and South, and the other crossing the same is the line of East and West, at the foure ends of which crosse Diameters you must set downe the foure principall windes, that is, East, West, North, and South, making the North parte with a flower deluce in the toppe, and the East parte with a crosse, as you may see in the figure following. Then divide everie quarter of the saide circle with your compasses into two equall partes, setting downe pricks in the middest of everie quarter, through which pricks, and also through the centre of the circle drawe two other crosse lines, which must extende

* Heathecote (89) quotes the directions given by Blundeville in "Blundeville

his Exercises," 1594, for constructing the portolano design.