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CONIC  PROJECTION - 14071_195
POLYCONIC  PROJECTION - 14071_197

Engineering Aid 2 - Intermediate Structural engineering guide book
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projection of the polar region is the fact that in the conic  projection,  the  cone  is  cut  and  flattened out to form the map or chart, whereas the gnomonic projection will appear as is. On the conic projection, points  lying  close  together  on  either  side  of  the meridian along which the cone is cut will be widely separated on the map. The gnomonic projection, on the other hand, will give a continuous and contiguous view of the areas. Figure 9-23 shows the appearance of meridians and parallels on a polar gnomonic pro- jection. CONFORMALITY According to some authorities, to be conformal, a   projection   must   possess   both   of   the   following characteristics: 1. It must be a projection on which direction is the same  in  all  parts  of  the  map.  Obviously,  for  this directional  conformality,  the  meridians  (which  indicate the direction of true north) must be parallel, and the parallels  (which  indicate  true  east-west  direction)  must be  parallel  to  each  other  and  perpendicular  to  the meridians. 2. It must be a projection on which the distance scale north and south is the same as the distance scale east and west. Obviously, none of the projections that we have described  have  both  of  these  characteristics.  The  only one that has the first characteristic is the Mercator. On this  projection  the  meridians  are  parallel,  and  the parallels  are  parallel  to  each  other  and  perpendicular to the meridians; therefore, the direction of north or east is the same anywhere on the map. With regard to the  second  characteristic,  however,  a  distance  of 15 degrees (for example) is longer in any part of the map  north-south  than  a  distance  of  15  degrees east-west (even in the same part). Figure 9-23.-Meridians and parallels on a polar gnomonic projection. 9-20







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