348 Forestry Quarterly. 



imposed upon his work in horizontal location, at the same time 

 however, local factors may so influence his work in obtaining 

 elevations with an aneroid that the vertical location will be de- 

 cidedly less accurate than his horizontal location. As a conse- 

 quence a large error is' introduced into the horizontal location 

 of the contour. 



The importance of the accurate horizontal location of con- 

 tours is apt to be overlooked when only the representation of 

 the general character of the topography is desired in the topo- 

 graphic map. Maps prepared by extensive methods, on a scale 

 of one or two inches to the mile, will be of this kind, and these 

 extensive maps will be consistently accurate because the horizontal 

 control and the vertical control are obtained with relatively equal 

 accuracy. If however, a map is prepared by supposedly intensive 

 methods the resulting map is more than a general representa- 

 tion of the ground and in order to give this technical character 

 to the topographic map prepared by intensive methods the com- 

 passman must appreciate the necessity for preserving the balance 

 between accuracy in vertical and accuracy in horizontal location. 



The accurate horizontal location of a contour is perhaps of 

 greatest importance to the timber appraiser, the logger, and the 

 trail and road builder. The minimum grade of a haul is de- 

 termined by the difiference in elevation between two points and 

 the horizontal distance between these two points. A topographic 

 map having this quality of consistent accuracy will show the 

 timber appraiser, logger and road builder a fairly accurate ap- 

 proximation of the grades within the limits of accuracy of the 

 map. An inconsistently accurate map will not, because the 

 horizontal location of the contour is not reliable. 



As a rule, in the construction of forest maps it is more dif- 

 ficult to get accurate results in the vertical location than in the 

 horizontal. The error in horizontal location can be corrected 

 and distributed between stations along the strip line so that 

 the final results will be well within the standard limits of ac- 

 curacy. Experience has demonstrated, however, that corrected 

 aneroid elevations, under some conditions, still exhibit an error 

 in vertical location, when compared with bench marks, out of 

 all proportion to the error in horizontal location. Under favor- 

 able circumstances, on the other hand, the elevations secured 



