6 INSTRUCTIONS FOR MAKING FOREST SURVEYS, ETC. 



errors usually balance themselves, and they are quickly 

 discovered by the trained operator, who will know how 

 to make allowance for them, if necessary. The 

 unskilled or careless man will sometimes read the wrong 

 end of the compass needle; read the graduated ring 

 dial from the wrong direction ; make a mistake in enter- 

 ing the reading in his notebook, or perpetrate some 

 other palpable blunder which will throw doubt over 

 the whole work and make a resurvey necessary. 



Certain fundamental principles underlie all surveys. 

 We may assume a piece of land the location, extent, and 

 contour of which are unknown. First of all the survey 

 should determine its location, shape, and area, and if 

 necessary its topography, and any other essential 

 data. As in logic, one should start from something 

 which is known to determine something which is 

 unknown. The line which connects an unknown point 

 with a known point is called a tie, and as soon as the 

 tie is run the position of the unknown point is estab- 

 lished. A line run around a tract of land is called a 

 boundary line, and the angles on this line are called 

 corners, stations, posts, or stakes, according to the local 

 or established terms. It is not always necessary to 

 run the boundaries of a tract to determine its position 

 and area. A base line might be run across it with ordi- 

 nates on either side extending to the limits of the tract. 

 Or if the tract is a small watershed, lines might be 

 traversed up all of the streams and drainage lines, or 

 the area might be divided into squares and fractions of 

 squares, similar to land-survey sections. Still another 

 way will be described under the head of "Plane table." 



