■ Mapping for Intensive Reconnaissance. 345 



are, in the best judgment of the topographer, the final contours 

 themselves. Intermediate form lines to show minor changes are 

 used only in exceptional cases, as their presence confuses the map 

 and there is' little advantage in putting indefinite data on the field 

 sketch which will be eliminated from the final map. 



It may be argued that, since only a limited portion of the area 

 he is covering is visible to the mapper, he should not attempt to 

 sketch in those portions which can not be seen. There is no rea- 

 son however to suppose that this part of the map can be supplied 

 any more accuately in the oflfice. The details are in the field, and 

 there the topographer has the advantage of being able to see at 

 least a part of the feature he wishes to represent, and from this 

 can make a reasonably good estimate of the unseen portion. In 

 the office it is a sheer guess. 



In order that the field sketch may be retained exactly as it is 

 turned in, a carbon copy is made and the corrected barometer 

 readings placed on it. The necessary adjustments are then made 

 on the copy. Such adjustments usually consist in a slight shifting 

 of some portions of the map in order to correct for errors in 

 bearing and distance, and to check up the contours with the cor- 

 rected elevations. It is very seldom that any change in the rel- 

 ative positions of the contours is required, and the finished map 

 loses none of the character of the original sketch. 



To sum up : — the first method encourages the use of the baro- 

 meter as a crutch, and bases its claim for accuracy chiefly upon 

 the accuracy of the barometer readings. 



Nothing definite, in the manner of representing topographic 

 data on the field sketch is required, and nothing definite is ob- 

 tained. 



Since it is the mechanical element that is emphasized, rather 

 than the personal there is little improvement in the quality of 

 the maps produced. 



By the second method the location of the contours is based to 

 some extent upon the topographer's judgment. The barometer 

 readings are used especially in making the final adjustments, 

 that is, backed by the best judgment of the topographer, as 

 well as by the barometer. 



Everv feature must be shown on the field sketch in a complete 



