PREVIOUS MAPS. 3 



The Survey of the Rocky Mountain Region, under Maj. J. W. Powell, 

 embraced an area of about 60,000 square miles, covering parts of Wyoming, 

 Utah, and Arizona. This work was done between 1869 and 1877. The 

 maps were drawn upon a scale of 4 miles to an inch, with contour intervals 

 of 250 feet. The work was controlled by triangulation from base lines 

 measured with wooden rods. It was carried on with a theodolite having a 

 10-inch circle reading by vernier to ten seconds, and was adjusted by the 

 method of least squares. Secondary triangulation was done with minute 

 reading instruments, and minor locations, together with topographic details, 

 were obtained by the use of the plane table. Heights were measured by 

 the barometer, supplemented by the vertical circle. 



The Northern Transcontinental Survey, an organization instituted by 

 the Northern Pacific railroad company for the survey and examination of 

 its lands, mapped, during the years 1882 and 1883, areas in Montana, Idaho, 

 and Washington, aggregating about 43,000 square miles. These maps were 

 intended for publication upon a scale of 4 miles to an inch, with contours 

 having vertical intervals of 200 feet. The work was based upon triangu- 

 lation, which was executed mainly with a theodolite having a circle 8 

 inches in diameter reading by vernier to ten seconds. The triangulation 

 was adjusted graphically. The topographic methods were quite similar to 

 those of the Hayden Survey. 



The U. S. ('oast and Geodetic Survey lias covered the greater pari of 

 the Atlantic, Gulf, and Pacific coasts with triangulation, and with a narrow 

 strip of topographic work. This strip is of variable width, depending 

 largely upon the configuration of the coast, being, as a rule, narrow where 

 the coast is simple, and broad where it is complex. Altogether an area of 

 nearly 40,000 square miles has been surveyed, the original sheets being 

 upon a scale of 1:10000 or 1:20000, the contours having vertical intervals 

 of 20 feet. Most of this work is directly available as finished work. Upon 

 some of it, however, the contours, .owing to the great age of the original 

 maps, have been obliterated, and it becomes necessary to resurvey this ele- 

 ment. In addition to its coast work, the geodetic work of this organization 

 has been extended into the interior in various directions, especially in New 

 England, and along the eastern border of the Appalachian Mountain system. 



