Is a spatial version of the classical Delphi, where “spatial” means that it is suitable for problems of spatial location. The method retains the consultation scheme of a panel of experts in several rounds, but the judgments/opinions of the panel of experts are expressed by placing points (k >= 1) on a map (called opinion-points), so that the questionnaire consists of a digital map in which experts are asked to indicate the most suitable point (or points) to solve the localization problem. The result of the first round is a map with a set of geo-referenced opinion-points on the study area, each with geographic coordinates (latitude and longitude) and each point represents a judgement of one expert with respect to the localization problem. In the following step the typical technique used in the classical Delphi relies on in the calculation of the interquartile range, which contains 50% of the judgements of the panel, with the aim of stimulating consensus. In the Spatial Delphi the interquartile range is replaced by an area, in the form of a circle, on the map. There is only one circle with a minimum radius, centered on one of the n points and containing 50% of the opinion-points. In the second round, the research question is proposed to the panel in the form of the same map with the addition of the circle of convergence. The experts are invited to remain within the circle. If an expert wants to place a point outside the circle, he/she is invited to give a reason for that choice. After the second round of consultation, a new circle of convergence is calculated, and the procedure is iterated until reaching a stopping criterion. If the consensus is triggered, in the end will be obtained a very small circle (compared to the region of interest) that represents the solution to the spatial problem. In real application, this method must be considered as a support to the decisions to be made in a spatial context, whose results represent the convergence of different informed spatial viewpoints.
