50 



SCIENCE. 



[Vol. X. No. 234 



The plan of work, the scale to be adopted, the methods to be 

 used with a view to efficiency, rapidity, and economy, were care- 

 fully considered, and then a plan was adopted, subject to such 

 modifications as experience should suggest. Although this plan, 

 and the progress of the work, have been set forth in various 

 official documents, nevertheless they seem to be very little known. 



It therefore appears desirable to set forth in brief and simple 

 form the plan which the Geological Survey has, after mature con- 

 sideration, adopted for making a topographic map of the United 

 States, and the progress which has been made in the prosecution of 

 the adopted plan. 



It was decided to make a map which, although primarily de- 

 signed for the use of the geological corps, should be upon such 

 scales and should represent such features as to make it subserve 

 all purposes to which a general topographic map is applicable, — 

 in short, that it should be the topographic map of the United 

 States. 



The question of the scale or scales of the map is one of the 

 utmost importance, as upon this depends, on the one hand, the 

 degree of accuracy and the amount of detail necessary to be ob- 

 tained in the survey, and, upon the other, the value of the map. 

 It was seen at once that it would be inadvisable to attempt to 

 make the maps of all parts of the country upon the same scale. 

 The differences in degree of settlement, in material wealth, in the 

 character of the prevalent industries, in the complexity of geological 

 phenomena, and in the amount and degree of detail of the relief, 

 all emphasize the desirability of varying the scale in different parts 

 of the country. 



A scale of i 162,500, or about one mile to an inch, was adopted 

 for the most populous regions, after a careful consideration of the 

 requirements which such a map should meet, and with full knowl- 

 edge of the experience of European nations in this matter. In the 

 southern and central States, the conditions of settlement, the 

 character of the industries, and other conditions, appear to admit 

 the use of a smaller scale, and accordingly for this area the scale 

 was fixed at i : 125,000 or about two miles to an inch. 



In the sparsely settled region of the Rocky Mountain plateau, a 

 still further reduction appeared advisable ; and for this region, with 

 the exception of certain small areas which for special reasons ap- 

 peared to require a larger scale, it was fixed at i : 250,000, or about 

 four miles to an inch. 



The maps represent all natural features of drainage and relief, in 

 degree of detail proportioned to the scale. They represent all 

 public culture, i.e., all such of the works of man as have relation to 

 communities as distinguished from individuals. This excludes, it 

 is true, a large part of the culture, but the portion excluded seems 

 for various reasons to be out of place upon such a map. It is of 

 little general interest ; it is evanescent, much of it to such a degree 

 that by the time the map is published it would be incorrect and 

 misleading. Its adoption would require the use of a large number 

 of arbitrary symbols, which would be unintelligible without an ex- 

 tensive legend upon each sheet ; and, furthermore, the inclusion 

 of so large an amount of cultural material would serve to confuse 

 the map and render its more important parts illegible. 



Relief is expressed by contours. The contour-interval, or, as it 

 may be designated, the vertical scale, is adjusted to the horizontal 

 scale, and to the degree of relief of the country. It ranges from 

 10 to 200 feet ; the smallest contour-interval accompanying the 

 largest scale, and vice versa. 



The size of sheets is so arranged that each sheet upon the small- 

 est scale comprises a square degree, i.e., a degree of latitude by a 

 degree of longitude. Upon the scale of i : 125,000, each sheet is 30 

 minutes in each dimension, and upon the scale of i 162,500, each 

 sheet is 1 5 minutes in each dimension. 



The field-work of the survey is carried on with direct reference 

 to the scale of publication. The accuracy, the amount of geometric 

 control, and the degree of detail of the sketching, are proportioned 

 to this scale. A greater degree of accuracy than is required is unde- 

 sirable, on account of the increased cost. A greater degree of 

 detail in the sketching than is demanded by the scale is not only 

 useless, but worse than useless, as it involves generalization in the 

 office in order to adapt it to the scale, and such generalization can- 

 not be as satisfactory as if made in the field. 



For convenience, the original maps and the plane-table sheets 

 are usually made upon scales larger than those of publication. The 

 following table shows the scales in use for the original platting of the 

 maps, the scales of publication, and the contour-intervals, together 

 with the areas surveyed in 1886, in the several areas of work : — 



Massachusetts 



New Jersey 



District of Columbia 



Appalachian 



Kansas 



Missouri 



Texas 



Arizona 



California 



Oregon . 



Montana 



Field- 

 Scale. 



• 63,360 



: 126,720 

 : 63,360 



; 126,720 



Publication- 

 Scale. 





[ : 250,c 

 [ : I2S.C 



■} and 40 

 ) and 20 



At the close of the year 1886, areas amounting to 250,000 square 

 miles, or about one-fourteenth of the area of the country, including 

 Alaska, had been surveyed. 



This work is carried on by a Division of Geography, having a 

 persojinel numbering about one hundred permanent employees 

 besides the temporary aids and camp hands employed during the^ 

 field-season. The organization of the division during the field- 

 season of 1886 was as follows : — 



TMassachusetts 4 topographic 



. < New Jersey i topographic. 



(.Dist. of Columbia i topographic. . 



opographic \ 

 nangulation / 



Appalachian y 



Centra, I^ansas {j ^^S^J^I^n } " 



(^Missouri I topographic 5 



fT-- V^o^^:) " 



Arizona. i topographic and triangulation 5 



Western California {nopoTaphir } ;- ' 



Oregon 2 topographic and triangulation 6 



[Montana ^ t'o'pog^aphic" } « 



The names given to the sub-sections indicate the fields of work, 

 and the number of men includes permanent assistants and tempo- 

 rary aids, but not laboring force. The work is everywhere con- 

 trolled by triangulation. Topographic work is prosecuted in part 

 by plane-table, using it by the method of intersections and by 

 traverse methods. Both these methods are in use in Massachusetts. 

 The work in the western part of the State is done entirely by plane- 

 table; that in the wooded, level country in the south-east, by 

 traverse, using the compass for direction and the telemeter for dis- 

 tance, elevations being measured by the vertical circle and by the 

 Y-level. In the north-east the two methods are combined to good 

 advantage, the work of the plane-table being supplemented by 

 telemeter traverses. In New Jersey the survey is made in plan by 

 traverse, with the compass and odometer. The vertical element is 

 subsequently added by Y-level. In the area adjacent to the Dis- 

 trict of Columbia, the survey is made by telemeter traverse. In the 

 Appalachian Mountain region, south of Mason and Dixon's line, 

 the triangulation rests upon the Appalachian belt of the U. S. Coast 

 and Geodetic Survey. The topographic work is in part done 

 by the plane-table, or the kindred method with the theodolite, but 

 mainly by traverse with compass and odometer. Elevations are 

 determined by barometer and the vertical circle. 



In Missouri and Kansas the work is greatly expedited by the 



