A Method for Making Topographic Maps 43 



These can be quickly and inexpensively made. The hole in the 

 peep sight should be about one-twentieth of an inch in diameter 

 and the one through which the cross-hair runs should be about 

 one-fourth of an inch. It is well to have one sight fixed and 

 the other adjustable so that the line of sight may be kept parallel 

 to the top of the board and consequently to the line cf. 



Any convenient material may be used for the board but it 

 is best to have a wood which works easily and which does not 

 readily warp, such as yellow poplar or white pine. The head 

 of the bolt which fastens the board to the staff should be sunk 

 so as not to obstruct the plumb line. The bolt should be at least 

 three-eighths of an inch in diameter to prevent bending. End 

 cleats on the board will help to prevent splitting and will lessen 

 warping. 



The staff should be cylindrical, about five feet long, and 

 about one and one-half inches in diameter. It should be so 

 turned at the top that a staff compass can be securely fitted on 

 the end. A sharp pointed metal shoe should cover the lower 

 end to enable the staff to be easily forced into the ground. The 

 board should be bolted as near the top of the staff as possible 

 without interfering with the compass. 



In the field, the party may consist of either two or three 

 men. In the case of a three-man party, one runs the instrument 

 and is rear chainman, another keeps notes and directs the work 

 while the third is rodman and head chainman. In case of very 

 irregular topography, where the elevations of many points are re- 

 quired, it is advisable that the instrument man keep notes while 

 the other two locate points for him and hold rods. In this way 

 several points can be taken rapidly from one set-up of the instru- 

 ment. If there are only two men in the party the instrument man 

 must add note keeping to his duties. A three-man party can do 

 more rapid work than a party of two and there is a more equal 

 division of labor. 



Where small areas, forty acres or less, are being surveyed, 

 the traverse of all or part of the area should be run first and all 

 bearings and elevations which control contours noted. Then, 

 such interior elevations as are needed may be taken. If the topo- 

 graphy is fairly uniform, points may be promiscuously taken by 

 running out from the traverse. If the topography is very irregu- 

 lar it is well to run lines at regular intervals across the tract 

 from known points on the traverse, obtaining the bearings and 

 elevations of critical points on the cross lines and near them. For 

 larger areas than a "forty," depending on the character of the 

 topography, it is usually best to establish a base line, preferably 

 at or near the middle of the tract. All necessary elevations 



