SADIE (Spatial analysis by distance indices) is a methodology and software for the exploratory analysis of spatial patterns. SADIE has been applied extensively since it was invented in 1995, especially in entomology. However, it has almost never been presented in the Chinese literature. The cornerstone of SADIE is distance to regularity, which is the basis for spatial randomness testing and association measurement. This article presents the algorithm for calculation of distance to regularity and the principles of spatial randomness testing, association measurement, and the red-blue plot for visualization of patchiness in detail. Methodologies for the diagnostics of aggregation, including IAF (initial and final) plot and EDF (empirical distribution function) plot are also included. Comparisons between SADIE and other traditional methods, and a review of the application of SADIE, are also provided.