Obtaining Control in Unsurveyed Townships. 379 



Base lines are now run in the ordinary manner. 



During the day's work the crew will be able to take sights upon 

 points of primary control. These angles are entered in the notes 

 and the day's work is handed in to the party chief in the evening. 

 The day's work in base line location is then plotted upon the 

 base plat. 



If the work of the base line crew has been inaccurate and care- 

 less, the sights upon points of primary control will not check. 

 The topographer has at all times a complete check upon the day's 

 work, both in horizontal and vertical location. All errors in base 

 line location are discovered before any further work is done. If 

 the day's work has been unsatisfactory, it is run over the next 

 day, and the error found. No errors will remain undiscovered 

 until after the strip crews have completed much of their work, 

 and errors discovered in the field at an early time, when they are 

 made, are more economical to correct than when they are dis- 

 covered in the main office. Herein lies one of the advantages 

 of such a system of resection and triangulation. 



The field work in obtaining primary control should always be 

 mapped as the work proceeds, and primary control should serve as 

 a clieck both for the field and office work. 



