44 Forest Club Annual 



should be taken on this line and bench marks established at regu- 

 lar intervals from which meander lines can be run to interior 

 points. 



Either the co-ordinate or the tabulated system of field note 

 keeping may be used. In the co-ordinate system a sheet of paper 

 is ruled off in squares. Each side of a square is scaled to the 

 horizontal distance ab required by the instrument, or some mul- 

 tiple of it, usually the latter. This sheet fastened to a field sketch 

 board takes the place of the ordinary field note book. It is usu- 

 ally desirable to record some actual measurements in addition to 

 roughly plotting them to scale and this can be done on unused 

 parts of the mapping sheet or in a note book. A protractor and 

 small scale may be carried in the field but it is usually sufficiently 

 accurate to roughly plot the points as in plane-table work. 



As the elevations are obtained they are immediately plotted 

 on the sheet and those points between which the slope is uniform 

 are connected by straight lines. For instance, two critical points 

 on a ridge should be connected. One of these would be connected 

 with a point at the foot of a valley and this with a point at the 

 head and so on until there is a network of triangles formed by 

 the connecting lines. Since the lines represent slopes which are 

 uniform, they can be interpolated for contours. For instance, 

 it is assumed that if the elevation at one end of the line is thirty- 

 two feet and at the other twenty feet, the difference in elevation 

 would be twelve feet. For every twelfth of the distance along 

 the line of the slope, there would be a change in elevation of one 

 foot, since the line is the hypotenuse of a right angled triangle 

 whose altitude is the difference in elevation. In this instance, if 

 the contour interval were five feet a contour would pass through 

 the point of twenty foot elevation, another would cross the line 

 five-twelfths of the distance and a third ten-twelfths from the 

 twenty foot point or two-twelfths from the thirty-two foot point. 

 Only these contours can cross this line and since all other contours 

 are controlled in the same manner by other connecting lines, no 

 confusion arises as to the course of contours. 



In transferring the field sketch to the final map sheet, tem- 

 porary co-ordinate lines of any desired interval are used, which 

 represent distances equal to those shown by the intervals of the 

 co-ordinate lines on the sketch map. The points and lines just 

 described are then simply copied in pencil from the smaller field 

 sheet. After the contours have been inked everything else may 

 be erased. Plate II is a sketch illustrating this system. 



The second system is the ordinary one of tabulating all data 

 in a field note book. Below is an example of such notes taken 



