1 870.] The Surveys of India. 457 



levelling operations of the Bevenue Survey with those already com- 

 pleted, or about to be prosecuted, by the Irrigation Branch of the 

 Public "Works Department. 



The field mapping is all executed on a scale of 4 inches to the 

 mile. 



In addition to the regular professional revenue survey of villages, 

 there has always been a minute measurement of fields for assessment 

 purposes, conducted by native agency, entirely under the collector 

 or settlement officers. These are crude operations after native 

 fashion. 



In the presidencies of Madras and Bombay, minute cadastral 

 measurements of fields are in progress under European officers; 

 these surveys are essentially for settlement and revenue pur- 

 poses, and have no connection with the Indian Survey Depart- 

 ment, nor are they under the direction of the Surveyor-General of 

 India. 



Topographical Survey. — The Topographical Branch of the In- 

 dian Survey Department is under the immediate superintendence of 

 the Surveyor-General of India, and had its origin in the Eevenue 

 Survey. Its operations are confined chiefly to hilly and jungle- 

 covered ground, yielding but little revenue, in parts of the country 

 not actually under British management, and in friendly native 

 states along the British frontier; and its object is to obtain a 

 cheap, rapid, and reliable first survey for geographical and admi- 

 nistrative purposes. The groundwork or basis of its operations is 

 secondary and minor triangulation dependent on the Great Trigo- 

 nometrical Survey operations, from which all the initial elements of 

 latitude, longitude, elevation, distance, and azimuth are derived. 

 The triangulation is carried on in a network covering the ground 

 with points or stations at about 3 to 4 miles apart. The instru- 

 ments employed for the secondary triangulation are vernier theo- 

 dolites with 12 and 14 inch azimuthal circles; the horizontal 

 observations are taken on four zeros repeated and the vertical 

 angles on two zeros. For the subsidiary or minor network of 

 triangles, theodolites with 7 and 8 inch azimuth circles are 

 used, and the angular measurements are made with two zeros 

 repeated. 



The detail work, or delineation of the configuration of the 

 ground, is executed usually on the scale of 1 inch to the mile by 

 means of the plane-table. Some topographical surveys in culti- 

 vated or valuable tracts are on a scale of 2 inches to the mile ; and 

 a few others, in very broken and wild ground, on a scale of 2 miles 

 to the inch. In addition to the 1-inch survey, the Topographical 

 Branch undertakes the plans of all the important cities, forts, and 

 strongholds in native states; these are mapped on scales varying 

 from 6 to 16 inches to the mile. 



