82 National Geographic Magazine. 



square miles. These sheets upon the scale of publication are 

 about 1*7^ inches by 13 in dimensions. In two or thi'ee cases 

 along the coast it seemed to be in the interest of economy to 

 vary from this arrangement slightly, in order to avoid the multi- 

 plication of sheets. Many of the sheets upon the borders of the 

 state project over into other states, and, in cases where the area 

 lying without the state was small, the survey was extended 

 beyond the limits of the state, in order to complete the sheets. 



Every map is a sketch, which is corrected by the geometric 

 location of a greater or less number of points. Assuming entire 

 accuracy in the location of the points, that is, assuming that the 

 errors of location of the points are not perceptible upon the 

 map, the measure of accuracy of the map consists in the num- 

 ber of these geometric locations per unit of surface, per square inch, 

 if you will, of the map. The greater the number of these locations 

 the greater the accuracy of the map, but however numerous they 

 may be the map itself is a sketch, the points located being simply 

 mathematical jDoints. Whatever method be employed for mak- 

 ing these geometric locations, the sketching is substantially the 

 same everywhere. The methods of making these locations must 

 differ with the character of the countr}^, as regards the amount 

 and form of its relief, the prevalence of forests and other circum- 

 stances. There are two general methods of making the geo- 

 metric locations used in surveying; one, bv triangulation ; the 

 other by the measurement of a single direction and a distance, 

 which is the method employed in traverse surveying. In prac- 

 tice, the two methods are often combined with one another. 

 Both methods have been employed in Massachusetts. The funda- 

 mental basis of the work was the triangulation which had been 

 carried over the state by the U. S. Coast and Geodetic Survey. 

 By this survey points were located at wide intervals over the 

 state. Besides this there was executed between 1830 and 1840,, 

 at the expense of the state, a triangulation known as the " Bor- 

 den Survey." This located a much larger number of points,, 

 but less precisely. The Coast and Geodetic Survey kindly under- 

 took the adjustment of this triangulation to an agreement with 

 its own work, and, as many of the lines were common to the two 

 pieces of work, the locations made by the Borden Survey were 

 by this adjustment greatly strengthened. Even after this work 

 was done, however, there remained considerable areas which 

 were destitute of located points, and it became necessary to sup- 



