LETTER OE TRANSMITTAL 



Department of the Interior, 



U. S. Geological Survey, 



Geographic Branch, 

 Washington, D. C, May 17, 1892. 



Sir: I have the honor to submit herewith for publication a manual of 

 the topographic methods in use by the Geological Survey, accompanied by 

 a collection of constants and tables used in the reduction of astronomical 

 observations for position, of triangulation, of height measurements, and 

 other operations connected with the making of topographic maps. It must 

 be understood that the methods are not fixed, but are subject to change and 

 development, and that this manual describes the stage of development 

 readied at present. 



In the preparation of this work I have to acknowledge the aid of many 

 of my associates, notably Mr. H. M. Wilson and Mr. S. S. Gannett. To 

 Mr. R. S. Woodward, now connected with the U. S. Coast and Geodetic 

 Survey, I am indebted for the " Instructions for the Measurement of Hori- 

 zontal Angles " in Chapter in. These instructions, which were drawn up 

 by Mr. Woodward several years ago for the guidance of field parties en- 

 gaged in primary triangulation, have resulted in a great increase in accuracy 

 and considerable economy of time and labor. To Messrs. G. K. Gilbert 

 and W. J. McGee I am indebted for their kindly criticism, especially con- 

 cerning the chapter upon the " Origin of Topographic Features." 



