TIMBER ESTIMATING. 43 
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 
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 tothe 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 exampie, 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 
