150 MICHIGAN ACADEMY OF SCIENCE. 



not relief of surface. Such maps are mere diagrams in two dimensions, 

 and take no account of the heights and shapes of mountains, the breadths 

 and depths of valleys, etc., or, in short, of any element of the earth'^s 

 surface rising above or depressed below an assumed plane. They are 

 not only devoid of expression, but to a great extent meaningless and 

 even misleading. When the pupil steps outside the schoolroom he finds 

 the region about him not a' featureless plain, as his maps have taught 

 him, but diversified in relief in many ways. 



The maps of Europe and the more modern maps published in America, 

 to which reference has been made, in addition to representing the rela- 

 tive positions of objects on the earth's surface, indicate with an equal 

 degree of accuracy the heights and shapes of mountains and hills, the 

 forms of valleys and the slopes of their enclosing uplands. In many 

 instances, the shapes of lake basins below the water's surface and of the 

 ocean's bottom are also quantitative]}' shown. In brief, such maps rep- 

 resent portions of the earth's surface in three dimensions, by means of 

 three co-ordinates, namely, latitude, longitude and height above or depth 

 below sea level. 



While map is a word generic in its significance and used to include 

 many species, as they may be termed, the j^articular species to which 

 attention is here invited, is the one on which relief of the surface is 

 represented, or the topographic map. On topographic maps there are 

 also presented in most instances, all of the data that can be shown on a 

 diagram, as, for example, political boundaries, roads, shore-lines, etc., 

 or the relative geographic positions of objects when reduced to a hori- 

 zontal plane. The significance of the word topographic in the above 

 connection is principally in reference to relief of surface. The term has 

 also acquired, by common consent, another significance, namely accuracij. 

 Maps on which attempts are made to show relief, are usually of such 

 a degree of excellence that accuracy in their construction has become a 

 chief reason for their existence. 



The demand for precision in the surveys on which topographic maps 

 are based, has become so rigid and the degree of skill required to present 

 it in final dress so great, that topographic mapping has developed into 

 a distinct branch of applied science, differing from other methods of sur- 

 veying. 



The successful topographer is not onl}' a surveyor but to no small 

 extent an artist. In his finished work, if well done, there exists, side by 

 side, nay in the same line, the accuracy of the geodesist and the expres- 

 sion of the landscape painter. A topographic map is a picture of a given 

 surface in which every part is precisely located in reference to three co- 

 ordinates. It is a representation, we will say. of a mountain from every 

 direction in which it may l)e seen. From such a map not only is a bird's- 

 eye view attainable of the region delineated, but from it one can read 

 distances, heights, depressions, and the slo])es or gradients of the sur- 

 faces of uplands and valleys. Nor is all told that may be read on such 

 a map, when the bare representation of the existing land surface is in- 

 teri)reted. With an accurate loi)ographic map of an extensive region, 

 such as a mountain range, or a river system, in hand, the geographer is 

 enabled to read between the lines, as it were, much of the geographic his- 

 tory of the area represented and to predict with a high degree of confi- 

 dence the changes that are to come. In skilled hands, an accurate topo- 

 graphic map becomes an instrument of research, and one that is indis- 



