Plane Table and Forest Maps 447 



to advantage. The latter location may allow many points over 

 the area to be located directly from the base, thereby eliminating 

 any accumulated error in triangulating. The length would de- 

 pend on the size of the country to be mapped and the accuracy 

 to which the measurement could be carried. For small areas, 

 a stadia traverse might answer, where it would be unnecessary 

 to expand the triangulation beyond the limits of locations from 

 this base. Such a base might be located by stadia traverse for 

 a distance of 10 miles, locating triangulation stations over the 

 entire area in the same operation. In general, a long base lo- 

 cated to a good degree of accuracy would be more satisfactory 

 than a short one where the attempt was made to measure to a 

 high degree of accuracy. There are few men familiar with accu- 

 rate base measurement who would be fit to undertake this work. 

 Another point is that in measuring the short base, nothing else 

 would be accomplished, while by the time the long base was 

 finished, practically all the primary control would be established. 

 In this case the base becomes practically a traverse. 



The choice of a system of control would, in the end, depend 

 on local conditions in each case. The U. S. Geological Survey 

 stations are the most accurate, are better located for use as 

 triangulation points, give a basis for horizontal control, and can 

 be platted more accurately. They are generally so far apart that 

 locations must be made on the field sheet on a small scale and 

 later enlarged, unless a transit be used. The land office corners 

 are more often available, a system of legal subdivisions is more 

 adapted to Forest Service needs, the meridian can be located 

 without special calculations, and, if recently established, offers 

 the choice of a great many different stations. The special base 

 would not be used if either of the other two methods were avail- 

 able. The method of locating the special base would also be 

 governed by local conditions. 



Platting on Map Sheets. — There is so much detail to be put 

 on forest maps that it is necessary to use large scale field sheets. 

 The scale of 2 inches equal one mile is large enough for abundant 

 detail, and still small enough to allow considerable area being 

 mapped on each sheet. The standard on intensive timber recon- 

 naissance is 4 inches equal one mile, but this is so large that 

 it causes not only too frequent changing of map sheets or joining 

 of sheets, but also shortens the sights materially so the full 



