Pencil Shading of Isopach Maps 



Shadow-graphic maps and the methods of drawing them have been described. 

 Similar use of a soft pencil can add much to the over-all legibility of isopach 

 maps, as shown in Figure 24-55. Thick areas are darkest, thin ones lightest. 

 About four different tones are most effective. The texture of the map paper 

 determines to a considerable extent the hardnesses of pencils that should be used. 

 On medium-weight Ozalid black-line paper, hardnesses of 2B to 2H are satis- 

 factory. The toning is accomplished by rubbing the graphite with a charcoal 

 stump blender, as described for indelible colored pencils. The change in tone 

 should be made along contours at equal thickness intervals. In the figure cited, 



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/ 



Figure 24-55. Isopach map shaded with pencil to emphasize areas of thick section. 



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