112 HYDROGRAPHIC MANUAL PaGE 2 



he tried to assign proper geographic positions and included in his work the mathe- 

 matical principles for the scientific construction of maps. He refers to maps which 

 are supposed to have been a part of his original work. At any rate maps were de- 

 lineated from his data a century or more later. 



During the next thousand years there was little progress in cartographic knowledge. 

 In fact there was retrogression, for the knowledge that the earth was a globe was 

 largely lost sight of and there was a return to the popular belief in its flatness. The 

 Crusades, the development of commerce by the cities of Italy, and a knowledge of the 

 properties of the magnetic needle, all combined to revive an interest in cartography 

 and led to the development of the Portolan Charts in about the fourteenth century. 



The Portolan Charts were intended primarily for the use of mariners, and Italy 

 and Catalonia, the two foremost maritime countries of the age, were principally respon- 

 sible for their development. They were compiled from the exploratory surveys of the 

 period but were most notable for the loxodromic, or rhumb, lines with which they were 

 covered. No projection was used in the construction of these charts but they were 

 generally drawn with considerable care. An attempt was evidently made to represent 

 the coasts of the various countries in mutual relationship to one another based on the 

 distances and courses actually run between points. The oldest Portolan Chart now 

 extant, which can be accurately dated, is credited to Petrus Vesconte in 1311. 



The era of exploration and discovery which immediately preceded and followed 

 the discovery of America by Columbus, and the invention of printing in the fifteenth 

 century, contributed to the renaissance of map and chart making in the fifteenth and 

 sixteenth centuries. It was during this era that Mercator published his well-known 

 world map in 1569, on the projection which bears his name. His was the first real 

 attempt to base a map on a mathematical projection. The meridians and parallels 

 are represented by straight parallel lines intersecting one another at right angles. 

 The meridians being equally spaced on this form of projection, the intervals between 

 the parallels of latitude are increased proportionally to compensate for the actual 

 convergence of the meridians on the earth. This projection is now almost universally 

 used for the construction of nautical charts, since it facilitates rhumb-line navigation. 

 Mercator was certainly the foremost cartographer of his generation and, in the opinion 

 of some, his projection is the greatest contribution of all time to the modern nautical 

 chart. 



112. The Nautical Chart 



A nautical chart is a reproduction, on a reduced scale, of some portion of the 

 navigable part of the earth's surface. It is a map constructed to serve the needs of 

 the mariner. It usually includes the adjacent land area, but its principal function is 

 to show the depths of the water and the menaces to navigation which are to be avoided. 

 It should emphasize the shore features of most use to the mariner and must include 

 all artificial aids to navigation. 



The earth's surface is spheroidal and any portion of it, no matter how small, is a 

 convex surface. For convenience in construction and use, the portion included on a 

 chart must be represented on a plane surface. Since it is impossible, even by curving it, 

 to make a flat piece of paper coincide with the surface of a sphere, it is obvious that 

 a strictly accurate representation of a portion of the earth's surface is not possible on 

 a piece of paper. Some distortion is inevitable, but the smaller the area embraced, 

 the less appreciable will be the errors of representation, until in harbor charts and others 

 of large scale and small extent these errors are scarcely measurable. 



