102 Henry Gannett — Mother Maps of the United States. 



and of widely differing degrees of accuracy, and the maps result- 

 ing therefrom differ in scale and value. 



It is my purpose to sketch the principal of these surveys, 

 characterizing the methods employed and the accuracy and value 

 of the maps which have resulted from them, in order to learn 

 what parts of the country have been well mapped, what parts 

 have been indifferently mapped, and what parts have not been 

 mapped at all. Such surveys have been executed under au- 

 thority of the general government and of state governments and 

 have been carried on by private enterprise. 



Surveys of the United States Government. 



The Coast and Geodetic Survey. — The most prominent organiza- 

 tion under the general government, and that one which is execut- 

 ing the most accurate work, is the United States Coast and 

 Geodetic survey, which, commencing its actual work in 1832, 

 has continued down to the present time. During this period 

 nea^rly the entire coast line of the Atlantic, Gulf and Pacific, with 

 the exception of the coast of Alaska,- has been mapped, together 

 with a strip of inshore topography ranging from half a mile to 

 five miles in breadth. The area of- topographic suryeys is not 

 extensive, being at the present date only about 34,000 square 

 miles. In addition to this work, triangulation has been extended 

 inland in various directions for a number of different purposes : 

 It has been extended southwestward along the Appalachian 

 mountains for the purpose of furnishing a suitable control for the 

 work along the southern coast ; it has been extended westward 

 from the Atlantic coast in the neighborhood of the 40th parallel 

 of latitude to central Kansas, and from the Pacific coast east- 

 ward to eastern Utah for the purpose of ultimately joining together 

 by triangulation the work upon the eastern and western coasts. 

 For assisting in state surveys, triangulation has been done in the 

 interior in many of the states, among which are New Hampshire, 

 Massachusetts, New Jersey, Wisconsin, Indiana, Kentucky and 

 Tennessee. Besides all this triangulation, numerous astronomic 

 determinations have been made in the interior. 



The triangulation of this organization is of the highest order 

 of excellence. Topographic details are mapped by the plane- 

 table. The planetable sheets are in the main made on a scale 

 of 1 : 10,000, or about 6 inches to 1 mile, and are published on 



