THE TOPOGRAPHIC SURVEY OF MICHIGAN. 



161 



pensable to those who seek to learn the laws governing our physical 

 environment. 



CONTOUR TOPOGRAPHIC MAPS. 



In searching for methods by means of which the relief of any region 

 may be represented on a plane surface, resort has been made to various 

 devices, such as brush shading, shading by means of short inclined lines 

 or hachiires, continuous lines drawn through points having the same ele- 

 vation or contours, etc. Of these various methods, the last mentioned, 

 namely, the use of contour lines, has by long experience and especially 

 when the question of expense is considered, been found the most satis- 

 factory by the majority of geographers. The contour topographic map 

 is without question the map of the future. 



By means of lines drawn through all points represented on a map, hav- 

 ing the same elevation or the same depression in reference to the assumed 

 datum plane, the shape of the surface in question may be accuratly por- 

 trayed. Such lines are termed contours, and a map on which relief is 

 shown by this method, becomes a contour topographic map. Contour 

 lines are few or many, according to the horizontal scale of a map, and 

 the degree of completeness with which it is practicable to indicate the 

 relief of the surface represented. The vertical distance between two 

 adjacent contour lines, or the contour interval, may be any measure, as 

 for example, ten, or one hundred feet. By this method not only can the 

 elevation of any point included on a map which is crossed by a contour 



Ideal Sketch and Corresponding Contour Map. 



line, be read at a glance, but the elevation of any ])oint between two 

 adjacent lines may be judged with a close approximation to accuracy. 



