568 JOURNAL OF FORESTRY 



Vertical control is carried over the forest by spirit-leveling. The 

 datum for this leveling is obtained from the nearest well-established 

 bench-mark, either of the U. S. Geological Survey or of the nearest 

 railroad. From this accurate spirit-level line vertical control is carried 

 over the base lines by Abney hand-level. 



Usually the base lines are a mile apart. 



Control on the strip lines is obtained by magnetic compass, steel tape, 

 and Abney hand-level. 



Subdivision of Labor. — Each crew is composed of three men. The 

 division of the work depends upon the character of the areas being 

 covered. Usually the strip crew is composed of two men — the com- 

 passman and the estimator; but when the stand is very dense the esti- 

 mator is assisted by a third man, called the computer. The computer 

 spends most of his time in the field office working up the tree measure- 

 ments and writing the results onto the forms provided for the com- 

 pleted timber estimates. 



Both the compassman and estimator correct their own maps and 

 place them on the office atlas sheets. It has been found that they can 

 do this much more accurately and quickly than can a camp draftsman 

 w^ho does not draw the map in the field. While either the compassman 

 or the estimator is thus engaged his place on the strip crew is taken by 

 the computer. In this way the strip-cruising work is carried on unin- 

 terruptedly. 



Camp and Travel. — Camp is made at the headquarters of the custo- 

 dian of the forest, and travel to and from work is done in Fords. This 

 is possible owing to the great number of roads and fire-lines on the 

 forests over which a light automobile can travel. As a result, the actual 

 time spent on strip line is increased very considerably over that possible 

 if the men had to walk to work. 



Scale. — The scale on which all maps are made is 12 inches to a mile. 

 This scale is not very convenient, since it is not easily converted into 

 chains. A scale of this size has been used on all the map-work done 

 on the forests previous to the present surveys and it is not considered 

 wise to change now. The large size of the scale, however, has many 

 advantages in mapping ; no undue crowding is necessary in order to 

 show all the details desired and ample room is left for corrections and 

 additions to the map. Furthermore, with the large scale there is no 

 need of exaggerating small important details out of all proportion in 

 order to indicate them, as is commonly done by the U. S. Forest Service 

 in its timber surveys. 



