The concept behind Ripley’s K-function.

Panel A: Ripley’s K-function is defined as the average number of events within a predefined radius of any event, normalized for the event intensity (density) over the whole field of view. A set of radii is typically used to quantify the scale at which clustering (or dispersion) of events occurs (red circles). Panel B: Events within a given field of view could be distributed in many forms, including Complete Spatial Randomness (CSR), regularity and clustering (with or without a diffuse pool). Panel C: plots for two of the event distributions in Panel B: CSR (upper) and Clustering (lower). The dashed lines represent the upper and lower critical quantiles (Q01 and Q99).