\ TIMBER ESTIMATING. 73 



DISTRIBUTION OF STRIP SURVEYS. 



There are two general methods of distributing the strip surveys 

 over a given tract; first, to lay them off in long strips running across 

 the tract, parallel and equidistant; and second, to locate them as 

 isolated sample areas. 



The Forest Service uses the strip method not only to obtain 

 estimates of the merchantable timber, but also to secure a count 

 of the trees not yet merchantable, to make forest maps, and to 

 gather other detailed information necessary for a practical forest 

 I Jl working plan. Under these circumstances lines of strip surveys 

 are usually laid off parallel and equidistant, and run across the 

 entire tract. Suppose, for example, that a township in the Adiron- 

 dacks is to be estimated. The first step is to determine the per- 

 centage of the area to be included in the valuation surveys and to 

 make a plan for their distribution. Usually one side of the tract 

 is chosen as a base line and the strips are laid off at right angles 

 to it and at equal distances apart. Stations are marked along the 

 base line to indicate the location of the strips. The crew starts 

 at the first station, near the end of the base line, and runs a line of 

 10-chain strip surveys across the tract in the chosen direction. At 

 the farther side of the tract the crew chains along the line the dis- 

 tance which is to separate the strips. Then a second line of strip 

 surveys is laid off parallel to the first, and running in the opposite 

 direction, to station No. 2 on the base line. As soon as the base 

 ^ line is reached the crew proceeds to the third station, when a new 

 * *strip is started parallel to the other two; and so on until the whole 

 tract has been covered. 



As the strip method is ordinarily used, the chaining is not done 

 very carefully. For example, the compassman may attach the 

 chain to his belt at the back and in walking forward mark off the 

 distances merely by scratching the surface of the ground with the 

 heel without marking by a pin or stake. Moreover, the chaining 

 usually is not done on a horizontal plane, but the lengths are 

 measured along the ground regardless of the slope. Thus, while a 

 valuation survey run up and down a steep slope will cover an acre 

 of surface, it is less than 10 chains long when projected on a map. 

 ^Because of this inaccuracy the strips often do not fit precisely into 

 the map, but there is small likelihood of any considerable error 

 from this lack of precision, because the errors in laying off single 



