The similarity maps show the spatial stratification of the quantitative similarities that result - always according to the preselected similarity measure (RIV, WIV etc.) - between a preselected atlas point ("reference point") and the remaining N-1 measuring points of the respective atlas grid. The reference point is selected by clicking (or activating) the polygon in question, whose surface remains white subsequently. The remaining N-1 polygons are colored according to the specifications of two interval algorithms (MINMWMAX and MEDMW) and using 2, 4, 6, 8, 10 or 12 color levels taken from the solar spectrum.
Note that among the mentioned N (= 641) inquiry points of the ALF there are 638 original points and another three artificial points which we had introduced for comparison purposes: 999 standard French (at the place of Paris), 998 standard Italian (at the south-south-east corner of France), 997 standard Catalan (at the southern tip of France in the department of Pyrénées Orientales).