To use inverse distance weighting interpolation to create a surface, there are several factors that cartographers need to consider. One important question is the type of relationship the phenomenon has with distance (e.g., does it decrease dramatically with distance, or do even relatively distant points have some degree of similarity with the non-sampled location?). Many cartographers choose to specify an inverse distance-squared relationship, where the weight of a point differs with the inverse square of distance (i.e., 1/distance2) rather than a simple inverse distance (i.e., 1/distance) (see Figure 6.cg.26, below).