Editing Stereographic projection (section)

===Geology===
[[File:Stero projection structural geology.png|thumb|300px|left|Use of lower hemisphere stereographic projection to plot planar and linear data in structural geology, using the example of a fault plane with a slickenside lineation]]

Researchers in [[structural geology]] are concerned with the orientations of planes and lines for a number of reasons. The [[Foliation (geology)|foliation]] of a rock is a planar feature that often contains a linear feature called [[Lineation (geology)|lineation]]. Similarly, a [[Fault (geology)|fault]] plane is a planar feature that may contain linear features such as [[slickenside]]s.

These orientations of lines and planes at various scales can be plotted using the methods of the [[Stereographic projection#Visualization of lines and planes|Visualization of lines and planes]] section above. As in crystallography, planes are typically plotted by their poles. Unlike crystallography, the southern hemisphere is used instead of the northern one (because the geological features in question lie below the Earth's surface). In this context the stereographic projection is often referred to as the '''equal-angle lower-hemisphere projection'''. The equal-area lower-hemisphere projection defined by the [[Lambert azimuthal equal-area projection]] is also used, especially when the plot is to be subjected to subsequent statistical analysis such as density [[contour line|contouring]].<ref name="Leyshon _&_Lisle_2004">{{Cite book |last1=Lisle |first1=R.J. |title=Stereographic Projection Techniques for Geologists and Civil Engineers |last2=Leyshon |first2=P.R. |publisher=Cambridge University Press |year=2004 |isbn=9780521535823 |edition=2}}</ref>
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