964 Subsurface Geologic Methods 



informed on the geologic developments, it devolves upon the geologist to 

 construct maps that convey the essence of his work in a direct manner, 

 without the details so necessary in the working maps. Maps tljat are to 

 be used for the purposes described above should emphasize the ideas and 

 conclusions of the geologist, not merely present or evaluate geologic data. 

 The methods of coloring maps have been described. But other fea- 

 tures of map construction are equally important. It is difficult to show 

 a number of different classes of geologic data on one sheet without some 

 confusion of lines or areas. Therefore, the legibility of the map should 

 be the principal guide as to how much can be shown to advantage. A 

 number of factors influence the legibility of a map: 



(1) Standard symbols — the U. S. Geological Survey has published 

 sheets of standard symbols for geologic maps. These symbols should be 

 used wherever applicable because they are more likely to be understood 

 by everyone using the map. If it is necessary to invent a symbol to indi- 

 cate some subsurface feature, this sheet of standard symbols should be 

 consulted to avoid using a figure which is standard for some other feature. 

 The size, form, and weight of symbols should be kept uniform, except in 

 special cases where a variation in the size or mass of the symbol denotes 

 a corresponding variation in the size or importance of the feature shown. 



(2) Line weights — the careful grading and uniformity of line weights 

 have much to do with the legibility and general appearance of the map; 

 for example, line weights should grade downward from state boundaries, 

 county boundaries, townships, sections, etc., despite the fact that certain 

 of these are further distinguished by various sequences of short and long 

 dashes. 



(3) Lettering — the lettering on most maps is done largely by LeRoy 

 or Wrico lettering sets. These guides are capable of producing letters in 

 a wide variety of sizes and line weights in both slanting and vertical 

 styles. The presentation of the map is greatly enhanced when the choice 

 of letter sizes and weights is made judiciously. Before any lettering is 

 done, the features should be classified, and proper templets selected for 

 each. The same templet will produce different-appearing letters when pens 

 of varying sizes are used. Likewise, the spacing between letters is im- 

 portant in the appearance of a name. It is good practice to employ wide 

 spacing for linear features and compressed spacing for locations of small 

 areal extent. Use slant letters for surface hydrographic features, such as 

 streams or lakes, and for descriptive or explanatory notations. Vertical 

 letters in upper and lower case are used for geologic and geographic 

 names. Large letters made with fine pens are less troublesome in obscuring 

 control points or figures than are small letters in heavy lines. Lettering on 

 vertical lines should read from the bottom upward. Lines that are even 

 slightly inclined to the left at the top are lettered from the top downward. 

 In other words, the letters should never be even slightly upside down. 



(4) Legends and Explanations — all symbols whose meanings might 



