A Method for Making Topographic Maps 



45 



when an instrument based on a horizontal distance of one hun- 

 dred feet is used: 



The tabulated note system is probably somewhat the more 

 rapid of the two in the field and might be preferred if the sur- 

 veyor plotted his own notes and had made explanatory sketches 

 of topography in the field. Such, however, is not always the 

 case and it is difficult for one who has never seen an area to 

 make a good map of it from the tabulated notes of another. 

 With the co-ordinate system as described above, the connecting 

 lines, to be interpolated, definitely control the drawing of contours 

 and the delineator does not have to depend on a first hand know- 

 ledge of the topography to make a correct map. 



The rapidity with which field work can be carried on de- 

 pends upon the size of the party, the contour interval, the pre- 

 sence or absence of trees and underbrush and upon the character 

 of the topography. As has already been stated, a three-man party 

 can do more rapid work than a party consisting of two. Like- 

 wise, an area can be more rapidly covered if the contour interval 

 is ten feet than if it is five or two feet since fewer elevations 

 will be required. Again, it is apparent that more rapid work can 

 be done on treeless areas than where trees and dense under- 

 growth obstruct the view.. In the latter condition shorter sights 

 must be taken and more or less clearing done. 



The average area actually covered per day with the instru- 

 ment by a two-man party has been determined for a treeless 

 area and for one densely wooded. The work on the treeless 

 area was in the sand hill region of Nebraska where the topo- 

 graphy is most difficult to map. The hills and valleys are small 

 and irregular and conform to no pronounced drainage lines. 

 Probably more than twice as many elevations were required on 

 this area as on one ordinarily encountered. The average area 

 covered by a two-man party was forty acres, the contour interval 

 being ten feet. Twice this amount would not be an extreme 

 estimate of what could be done on a more favorable area. 



