570 JOURNAL OF FORESTRY 



field in lieu of contours to show the form of the ground, and from 

 which, later, contours are drawn — is practically impossible. The 

 trigonometric computations by which elevations are determined are 

 checked over at the end of each half mile of strip-line run. Mathe- 

 matical errors are thus detected and corrected before the errors are 

 carried far on the strip. 



Compassmen are likely to read the angle measured with the hand- 

 level with the wrong sign — that is, read an angle plus when it should 

 be read minus, and z/ice versa. This is the common error in the work 

 in this region, for owing to the nearly level land the correct slope of 

 the ground is not apparent to the eye. A second Abney level reading, 

 taken by either the computer or the estimator, usually serves to correct 

 the incorrect reading made by the compassman. 



As soon as a section (640 acres) has been mapped, the compassman 

 spends in the office the time necessary to correct his maps, fit them to- 

 gether, and put them on the office atlas sheets, at least in pencil. It is 

 the earnest effort of the crew to keep the office work as nearly abreast 

 as possible of the field work. The field work is checked over in the 

 office, at least sufficiently to indicate the presence or absence of any 

 slips in the field work. If incongruities are found or unexplainable 

 irregularities of delineation are detected, they are then corrected or 

 explained immediately, while the region is still fresh in mind ; for since 

 there are few pronounced lines of drainage, it is next to impossible in 

 most cases to approximate where contour lines or type lines should be 

 drawn. One contour line cannot be used as an indicator of the location 

 of the next contour. 



The field-map form is about 8 inches by 12 inches in size and it is 

 held in a binder (the "tatum-holder" of the U. S. Forest Service). It 

 is ruled so that 160 acres may be mapped on it. On the same sheet 

 and underneath the map are four ruled lines. On each line are re- 

 corded the measurements, distance, and elevation obtained during the 

 course of the strip through the quarter section. Since there are four 

 strips through each 160 acres, the record is directly under the strip to 

 which it applies. This scheme has proved to be of considerable assist- 

 ance in recording and applying measurements and in checking the work. 



SITE MAP 



A map of the quality of the forest sites is especially important to the 

 State Forester in two ways, namely, (i) in the application of yield 

 tables in the computation of the value of the future crops of timber, 



