THE TOPOGRAPHICAL SURVEY OF INDIA. 2$l 



plane-tabling depends, and the accuracy with which 

 (when suitable precautions are taken) it can be applied 

 as a method of observation subsidiary to the ordinary 

 trigonometrical processes. 



' A hilly country,' says Sir A. Waugh, offers the 

 fairest field for the practice of plane-table surveys, 

 and the more rugged the surface the greater will be 

 the relative advantages and facilities this system pos- 

 sesses over the methods of actual measurement. On 

 the other hand, in flat lands the plane-table works at 

 a disadvantage, while the traverse system is facilitated. 

 Consequently, in such tracts, the relative economy of 

 the two systems does not offer so great a contrast as 

 in the former. In closely wooded or jungly tracts, all 

 kinds of survey operations are prosecuted at a disad- 

 vantage; but in such localities, the commanding points 

 must be previously cleared for trigonometrical opera- 

 tions, which facilitates the use of the table.' 



In whatever way the topographical details have 

 been filled in, a rigorous system of check must be 

 applied to the work. The system adopted is that of 

 running lines across ground that has been surveyed. 

 This is done by the head of the party or by the 

 chief assistant-surveyor. A sufficient number of 

 points are obtained in this way for comparison with 

 the work of the detail surveyors ; and when the dis- 

 crepancies exceed certain limits, the work in which 

 they appear is rejected. Owing to the extremely 

 unhealthy, jungly, and rugged nature of the ground 

 in which nearly all the Indian surveys have bee 



