W -hV 



Figure 25-1. Sphere showing stereographic projection of plane by both cyclographic and 

 Polar projection. 



circles, when projected to the zenith, will trace arcs on the equatorial plane and 

 form the latitudinal lines observed on the stereographic net. 



The beginner will note that to measure angles along a radius in the plane 

 of the net it is first necessary to orient the radius to a north, south, east, or west 

 direction. The small distortions in most stereographic nets may cause an error 

 of one or even two degrees, but this is well within the limit of accuracy of the 

 basic data. 



Polar Projection 



In Figure 25-1 the plane is represented on the stereographic net by a line 

 through the center in the direction of strike and an arc which is the projection 

 of the great circle cut by the plane. This is cyclographic projection. However, 



532 



