CARTOGRAPHY OF THE GREAT DISCOVERIES 79 



years of the sixteenth century that scales of latitude are found 

 on marine charts, so that until then the charts which recorded 

 the Portuguese advance along the African coasts continued 

 to display the features of the Mediterranean portolan charts. 

 Since the coasts they were charting ran for the most part in a 

 southerly direction, this was not at first a source of great 

 difficulty, though the influence of magnetic variation was not 

 appreciated. It had been observed on land, but its calculation 

 at sea was not seriously undertaken until the next century. 

 When it became necessary to chart accurately a number of 

 points, situated for example on each side of the Atlantic and 

 extending through many degrees of latitude, the neglect to 

 take account of the convergence of the meridians rendered 

 the old type of chart extremely inaccurate. The task before 

 the pilots at this stage was still largely to set down distance 

 and direction as accurately as possible, but when we examine 

 the charts which have survived, for example, Andrea Bianco's 

 at the beginning of the period (1448) and Graciosa Benincasa's 

 chart of the discoveries some distance beyond Sierra Leone 

 (1468), we have to conclude either that they were very care- 

 lessly assembled from sectional charts, or that accuracy of 

 distances was forfeited for some other purpose. Benincasa's 

 chart portrays the coast on a scale which increases steadily 

 southwards, the scale of the most southerly portion being nearly 

 four times that of the northern. Now the northern portion of 

 the coastline is featureless in contrast to the estuaries and 

 islands further south, and it is possible that the diversified 

 coast was deliberately drawn on a larger scale. A similar 

 variation in scale and emphasis on prominent features are 

 characteristic also of Bianco's chart. In the brief reference 

 above to methods of navigation, the extent to which landmarks 

 were employed in coastwise sailing has been pointed out, and 

 by this enlargement of scale features were made more easily 

 recognizable. The descriptive names used on the charts served 

 the same purpose. 



When the latitudes of a number of places on the African 

 coast had been fixed, it became less necessary to emphasize 

 particular stretches in this way, for the navigators were not 

 tied to coastwise sailing. In rounding the Cape, for example, 



