12 



A MANUAL OF TOPOGRAPHIC METHODS. 

 Statistics of control, field season 1891. 



Area surveyed, square miles 



Triangulation .stations 



Number of square inches per station 



Points located by triangulation 



Triangulation stations and located points 

 Number of above locations per square inch 



Number of miles traversed 



Inches traversed per square inch 



Number of traverse stations 



Traverse stations per square inch 



Total number of locations per square inch 



Traverse stations per linear mile 



Ilciulits measured instrumentally 



Heights measured by aneroid 



Total number of measured heights 



Heights per square inch 



Northeast Southeast 



division, division, 



New Appalachi- 



England, an region 



New York, and 



and I'enn- Atlantic 

 sylvan: 



5, 700 



j.; 880 

 29. 586 



113,500 



50. 1 



56 680 

 28. 



Central ili\ ision. 



1,276 

 4,034 

 5, 310 



:: 150 



1 



1,4X0 



8 



40. :s 



20, 760 

 50.1 

 50.1 



As the reader will observe, the amount of control of various sorts is 

 given in the above table with reference to areas in square inches upon the 

 map as published, it is given in these terms in order to eliminate from it 

 the question of scale. 



No statistics of horizontal control are given for the areas surveyed in 

 Wisconsin, Illinois, and Kansas, because most of it is furnished by the 

 survevs of the General Land Office, and therefore the presentation would 

 be but a partial one. 



There are two general methods for location of stations and of minor 

 points for the correction of the sketch, the one by angular measurements 

 (triangulation), the other by measurement of directions and distances, 

 or what is known popularly as the traverse or meander method. In ordinary 

 practice, work may be done by either of these two methods, or they may 

 be used in conjunction. The former of the two methods may be carried on 

 with the plane table, various forms of the theodolite, with a compass, or, 

 indeed, with an angle-reading instrument. The latter method may be car- 

 ried on with the same instruments, supplemented by various forms of odom- 

 eters, chain, steel tape, stadia, etc., for the measurement of distance. The 

 first method, whenever it can be used economically, is the most accurate, 



