1000 



Subsurface Geologic Methods 



tional representation is made or projected on vertical planes parallel to 

 ordinate lines. All sections are prepared as if facing in either a northerly 

 or easterly direction. Sections are prepared in a manner that lateral 

 boundaries coincide with the boundaries of the above-described plan unit- 

 area rectangles of the same scale. This manner of preparation is so that 

 sectional data may be filed with the plan data of the same unit area. Sec- 

 tions must not laterally overlap from one "quadrangle" to another because 

 confusion in indexing and filing will result. 



East- West Sectional Grid— This grid, which is identical to the plan 



a b 



Figure 527. (a) Relationship of east-west sectional unit area to plan unit area; (b) 

 relationship of north-south sectional unit area to plan area; (c) correlation of 

 diagonal sectional boundaries with plan area boundaries. 



grid, is erected in a vertical plane of east-west orientation in such a manner 

 that the long dimension of the rectangle is vertical. The east and west 

 borders of the sectional map areas are made to coincide with the east and 

 west borders of the unit plan-areas. The elevations of the top and bottom 

 borders of the 50' scale-unit sectional areas are made to coincide with ele- 

 vations evenly divisible by 500 (fig. 527a). 



North-South Sectional Grid — A grid in a vertical plane of north-south 

 orientation is erected with the short dimension of the rectangle vertical. 



