36 Report on the projected Survey of the State of Maryland. 



defect there might exist of this kind. The difference, too, between 

 the area afforded by this projection and that derived from the calcu^ 

 lations of the Rhumbs is so minute as to prevent any distortion from 

 taking place or the formation of any false ideas as to the relative posi- 

 tions of different places. 



The proportion of the map to the actual extent of country inclu^ 

 ded in its hraits is as 1-200,000 ; that is to say that every measure- 

 ment on the map is intended to be the l-200,000th part of a similar 

 actual measurement. 



These proportions and projections had been adopted before any 

 thing definite was known of the progress of the coast survey of the 

 United States, which is now proceeding under the direction of M. 

 Hassler 5 several considerations however would now dictate the adop- 

 tion of a projection uniform with whatever may be decided on for 

 the larger survey. With regard to the proportion it is a matter of 

 smaller importance ; since the detailed surveys hereafter to be en- 

 tered upon, will exhibit results the l-2000th of actual dimensions ia 

 length, and it will be practicable to reduce with the greatest accura- 

 cy, whatever part may be desired, to any given scale. The defect, 

 too, in the present map, of minuteness of scale, will be remedied ia 

 the Atlas, which it is proposed to arrange, of the counties, upon a 

 proportion of l-50,000th, or four times the present dimensions. 



With regard to the profiles, which are given on the face of the 

 map, and whose horizontal and vertical proportions could not be made 

 the same, while the scale of miles is the same as on the map, the 

 vertical measurements are the 1 -4000th part of the real elevations. 

 A solitary exception will be found in the case of the Chesapeake and 

 Ohio Canal, which for convenience was reduced to one half in the 

 horizontal proportions. It has been endeavored to apply the results 

 of these profiles to the horizontal face of the map ; and the dotted 

 lines which are already familiar to every reader of nautical charts, as 

 denoting elevations of reefs or depths of soundings, have been trans- 

 ferred to indicate similar circumstances on land. The lines, for the 

 sake of avoiding confusion, represent planes which are supposed to 

 lie each one hundred feet above the other ; a nearer approximate ele- 

 vation of any point, is obtained by noticing its distance from the level 

 line nearest it. The elevation always bears to one hundred feet the 

 same proportion that the distance observed does to the entire distance 

 between the two dotted lines enclosing the place whose elevation is 

 sought. 



