OCEAXOGRAPHIC INFORMATION FOR SUBMARINE CABLES 1057 



cases can be traced to either gross mistakes in plotting or poor accuracy 

 in na\'igation which may cause errors in position of up to 25 miles. 

 Usuall3' these gross errors are fairly easy to spot. For example, a large 

 shoal area was shown for many years in deep water east of Georgia, but 

 it now appears that this particular shoal resulted from the misplotting, 

 by one-half degree of longitude, of a series of continental shelf soundings. 



Lines of soundings from different sources should indicate the same 

 depth at their intersections, providing a check on the reliability of 

 both or an indication that one or both is suspect. Where there is lack 

 of agreement the sounding and navigational methods should be checked 

 in an effort to find a basis for choosing one set of soundings rather than 

 the other. However, without special knowledge about the individual 

 sounding lines, it is often impossible to decide which line is correct. 

 I'ncertainties of 2 to 25 miles in position combined with possible errors 

 in depth determination of 10 per cent and possible gross errors in plotting 

 are indicative of the difficulties that may be encountered. 



The extent of the coverage of the Atlantic Ocean with precision sound- 

 ing tracks is shown on Fig. 3. Sounding tracks taken by the Lamont 

 staff prior to the availability of the PDR are shown on Fig. 4. 



2.3.3 Methods of Presentation 



Relief is usually indicated on maps and charts by any one of a number 

 of devices, including contour lines, profile views, and physiographic 

 sketches. In contouring, after surveying a number of control points and 

 obtaining their exact elevations, the land surveyor sketches in the con- 

 tour lines between control points while standing on a ^'antage point such 

 that he can actually see the terrain. In contrast, the oceanographer must 

 sketch contour lines by applying his own interpretation of the submarine 

 processes responsible for the relief in the areas between soundings. The 

 accuracy of contour is, of course, determined by both the number, spac- 

 ing, and accuracy of the soundings, and the skill and knowledge of the 

 oceanographer. 



The International H3^drographic Bureau in Monaco publishes a 

 colored contour chart for the entire world on a scale of 1 : 10 million, 

 individual sheets of which are revised and republi-shed at 10-25 year 

 intervals. 



Profiles, or elevation views along particular tracks, provide a detailed 

 outline of the bottom. The usual practice is to construct exaggerated 

 profiles (-40:1 or greater vertical to horizontal scale ratio), such as 

 those illustrated in Figs. 2(c) and 5. Where accuracy of the highest order 



