TOPOGRAPHICAL MAPS OF THE STATE. 237 



the cost of the triangulation about one half. The exact determination of the principal 

 points over the state, in this way, lies at the foundation of a correct map. The town 

 maps and all the details can be prepared with more or less fulness and correctness, as 

 may be convenient, and the state map improved from time to time till it is perfect, if 

 the expense cannot be incurred at once. Slight errors in the position of the details 

 would not greatly injure the map if the main points were all correct. But a map 

 compiled from the best town surveys could not be relied upon as accurate. There 

 would be likely to occur errors of some miles. In the copy of Carrigain's map now 

 before me, by comparing the position of several points with their actual position as 

 determined by the U. S. Coast Survey, they appear to be from ten to fifteen statute miles 

 out of the way in longitude, and from one third of a mile to a mile in latitude. The 

 large error in longitude has been partially corrected on later maps. The relative error 

 is also considerable, though not more than what might exist in any map made in the 

 same way. For instance, if Fort Constitution be assumed as correct in position, 

 Uncanoonuc is more than a mile too far north and half a mile too far east, while Mt. 

 Washington is two thirds of a mile too far south, and one third of a mile too far west. 

 What remains to be done, then, to obtain the required data for an accurate map, is to 

 complete the triangulation of the state, and make a correct plan of all the towns and 

 places that have not yet been accurately surveyed. 



Improvements Incorporated into the New Map. 



Survey of the northern boundary by the United States government, in 

 accordance with the treaty of 1842. Noticed upon pages 21, 171. 



Operations of the United States Coast Survey south-east of a line from 

 Mt. Washington to Mt. Monadnock. 



Triangulation of several points under the direction of the geological 

 survey in 1869. See full report further on. 



Triangulation of the geodetic connection survey under the direction of 

 the United States Coast Survey, E. T. Ouimby, acting assistant. See 

 page 47. 



County maps. From 1855 to i860 careful odometer surveys were 

 made of every county in the state, and the results published by subscrip- 

 tion. The scale was usually about an inch to the mile; and the most 

 valuable portions of them relate to the delineation of the highways. 

 Existing surveys of lakes, water-courses, boundary lines, railroads, and 

 other topographical features were made use of wherever practicable. A 

 map constructed simply from these odometer maps would produce a new 

 draft much superior to Carrigain's, for the number of surveyors is greatly 

 reduced, and there is consequently less opportunity for discrepancies 



