A METHOD OF OBTAINING MAIN CONTROL IN UN- 

 SURVEYED TOWNSHIPS. 



By William J. Paeth. 



Since all maps are sketches controlled by locations, it is es- 

 sential that the points of control be accurate locations. This ap- 

 plies most strongly to the points of main control. The sup- 

 plementar)' control is not so important because all the errors 

 in location are corrected by tying in upon the main control. Al- 

 though the construction of Forest Service maps does not call for 

 a very high degree of accuracy, it is essential that the main con- 

 trol be obtained with as much technical precision as possible 

 with the methods available. With a good main control a prac- 

 tical accurate map is secured, although the methods employed 

 in obtaining the secondary control may be very^ rough and in- 

 accurate. 



This method of obtaining main vertical and horizontal con- 

 trol is applicable only in high country where triangulation stations 

 can be erected cheaply on high peaks frequently visible through- 

 out the forested area. A township surrounded by prominent 

 peaks, and having some natural prominent points also within its 

 limits, will adapt itself to this method, provided there are small 

 open areas, big meadows, burned areas and barrens. From these 

 points the sights necessary can be secured- 



Horizontal Primary Control. 



When available the U. S. Rectangular Surveys furnish accurate 

 horizontal main control for the construction of practical Forest 

 Service maps. 



It is essential that the character of the control be clearly under- 

 stood before plotting the control secured from these surveys upon 

 the base plat. 



The object of the U. S. Rectangular Surveys is primarily legal 

 land subdivision. The theoretically ideal township is a trapezoid. 

 The eastern and western meridians forming the eastern and 

 western boundaries' on the township converge about 65 links to the 

 township in this latitude, 43 °N. This error is thrown into the 



