Most general spatial analyses assume isotropy. Isotropy is the condition with the same spatial pattern in all directions. Anisotropy (or directionality) is the condition with different spatial patterns in different directions. The following figure illustrates a simple case of isotropic and anisotropic point patterns. Anisotropy is discussed in more detail later.
Examples of isotropic and anisotropic point patterns. In the left box, the points are arranged randomly with respect to direction within each cluster. In the right box, the points within a cluster are aligned in a NW to SE direction.