Subsurface and Office Representation in Mining Geology 1001 



The north and south borders of the sectional-unit areas coincide with the 

 north and south borders of the unit plan-areas. The elevations of the top 

 and bottom borders of the 50' scale-unit-sectional areas are made to coin- 

 cide with elevations evenly divisible by 400 (fig. 527b) . 



Oblique Sectional Grid — Vertical sections, diagonal to the ordinate 

 lines, are prepared in a manner similar to the north-south sections. The 

 northwest or southwest boundaries of the sectional unit areas are made 

 to coincide with the west (or, if necessary, with the north or south) unit 

 plan-area boundaries which are traversed by the lines of section. That 

 portion of any note-sheet area which extends across the boundary into an 

 adjacent unit-plan area is not utilized; a new sheet is prepared for this 

 portion of the sectional area. The elevations of the top and bottom of the 

 rectangles are made to coincide with elevations evenly divisible by 400 

 (fig. 527c). 



Office-Map Grid System — The ofl&ce-map grid system is based on the 

 same principles as the note-sheet grid system. Ten unit note-sheet areas 

 of any standard scale combine to form a unit office map area. The office- 

 map grid system is based on the combination of ten 8"x 10" note-sheet 

 areas to form a map area 20"x 40". If two east-west tiers, of five 50' scale 

 note-sheet areas in each tier are combined, the resulting 50' scale office-map 

 rectangle is 1,000' wide in a north-south direction and 2,000' long in an 

 east- west direction. (See fig. 530.) Standardized sheets of 20" x 40 "map 

 area are used for all scales of office representation — sectional and planar. 

 Large-scale office-map areas are even multiples of small-scale map areas 

 (fig. 531). 



The north and south borders of the 50' scale unit office-map areas are 

 made to coincide with north-regional-ordinate values evenly divisible by 

 1,000. The east- and west-ordinate values are evenly divisible by 2,000. 



The ordinate values of the north and south boundaries of 200' scale 

 map areas are divisible by 4,000, and the east- and west-boundary ordinate 

 values are divisible by 8,000. 



Similarly, the ordinate values of the north and south boundaries of 

 1,000' scale map areas are divisible by 20,000 and the east- and west- 

 boundary ordinate values are divisible by 40,000. 



North-ordinate values of the 5,000' scale-map boundaries are divisible 

 by 100,000, and the east-ordinate values are divisible by 200,000. 



Sectional Office-Map Grid System — In most respects the office-map 

 sectional grids are the same as the previously described note-sheet sec- 

 tional grids. 



East-West Sectional Grid — East-west office sectional unit-areas are 

 oriented so that the long or 40" dimension of the rectangle is in an east- 

 west direction, and the east and west borders of the sectional map areas 

 coincide with the borders of the plan map areas of the same scale. The 

 elevations of the top and bottom borders of the sectional rectangle are 

 always evenly divisible by 1,000 (fig. 532) . 



