What is crystallographic equivalence?
Directions &amp; sites are said to be crystallographically equivalent, because there are symmetry operators that relate them.  So 


learn about simpler symmetry operations (proper axes, mirror planes, centres of inversion) or advanced ones (like screw axes, glide planes, etc.)
learn how to recognize them in every-day's life.  It may be helpful for crystallography, and in other fields too: IR / Raman spectroscopy, for example, not only for understanding (descriptive), but for forcasting (predictive).  Tutorials like this represent an entry.