358 Forestry Quarterly. 



profile of streams and valley lines expressed in degrees or per 

 cents of slope. 



When the line crosses a stream the compassman plots the di- 

 rection of the stream upon his map sheet. If he carries an 

 aneroid alone the office man gets only an idea of the horizontal 

 location of the stream. The compassman equipped with the 

 Abney hand level after having plotted the stream on the map sheet, 

 takes a sight straight down stream and up stream. He then enters 

 upon his map sheet the gradient of the stream, valley or draw. 

 From this data the office man can calculate the drop of the 

 stream or valley in feet and he can plot the exact location of the 

 contours crossing the stream bed. The final map will show the 

 true character of the stream, valley or draw with more accu- 

 racy than a map prepared from less detailed vertical control data 

 with the aneroid. 



The compassman also notes the difference in elevation between 

 a ridge, peak, lake, etc. and the point of observation on the line. 



Often low leaks, lakes and spurs or ridges lie to one side of the 

 line. The compassman sights to the top of the peak or point of 

 the ridge, and obtains the vertical angle or per cent of the slope 

 to that point with his Abney. The point is located horizontally 

 by intersection. The absolute elevation of the point is not neces- 

 sary to the man in the field. The field man only determines the 

 difference in elevation between his position on the line and the 

 point sighted at. The sight is plotted so that the man in the office 

 will know from what position on the line the sight was taken. 



In the same manner, the difference in elevation between lakes, 

 valleys, draws, etc., and the position on the line can be determined. 

 The sights are all plotted on the map and the difference in elevation 

 in feet entered on the line indicating the sight as either a plus or 

 minus difference. The man in the office, when he calculates the 

 elevation of the point, of observation on the strip, then adds this 

 diflference of elevation to secure the absolute elevation of the 

 point sighted at. 



It can not be too often repeated that the field man does not 

 need absolute elevations to draw sketch or form lines. The dif- 

 ference in elevation between his position and the points to one side 



