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--- determine_weights_of_evidence_correlation [2013/08/12 18:18]
admin
+++ determine_weights_of_evidence_correlation [2026/08/28 03:17] (current)
hermann Sync from local documentation review
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 ====== Determine Weights Of Evidence Correlation ======
 ===== Description =====
-This container calculates the correlation between a pair of maps.
+This container calculates the correlation between pairs of spatial variables used in a Weights of Evidence analysis, to help verify that they are spatially independent, an assumption the Weights of Evidence method requires. Correlated variables identified this way can be eliminated, or combined into a new variable that replaces both.
+This container accepts one or more [[Name Map]] hooks nested inside it, each assigning a name to a map. These named maps supply the values for the spatial variables referenced by Ranges.
 ===== Inputs =====
-^ Name ^ Type ^ Description ^
+^ Name  ^ Type  ^ Description  ^
-| Ranges  | [[ Weights Type|Weights  ]]  | Pre-defined intervals for continuous gray-tone variable.  |
+| Ranges  | [[Weights Type]]  | Pre-defined ranges for each spatial variable whose pairwise correlation will be calculated.  |
-| Transition  | [[Transition Set Type|Transition Set  ]]  | A specified transition.  |
+| Transition  | [[Transition Set Type]]  | Transition for which the variables and ranges are defined.  |
 ===== Optional Inputs =====
+None.
 ===== Outputs =====
-^ Name ^ Type ^ Description ^
+^ Name  ^ Type  ^ Description  ^
-| Report  | [[Table Type|Table]]  | Table containing a full report of correlation calculation. These are essentially the same results showed in the message log, but in a table format.  |
+| Report  | [[Table Type]]  | Table with the same information reported to the message log during the calculation: for each pair of variables, the columns "Transition_From", "Transition_To", "First_Variable", "Second_Variable", "Chi_2", "Cramer", "Contingency", "Joint_Entropy", and "Joint_Uncertainity".  |
 ===== Group =====
@@ Line 22: / Line 26: @@
 [[Functor List#Calibration | Calibration]]
 ===== Notes =====
-When considering the advantages of Weights of Evidence over other statistical methods, such as Logist or Linear Regression, one can mention that it is not constrained by the classical assumptions of parametric methods, which spatial data often violate. Furthermore, the effect of each spatial variable can be calculated independently of a combined solution. The only assumption that must be made is that the predictive maps are spatially independent, which can be tested using pairwise tests for categorical maps, such as the Cramers Coefficient, Contingency Coefficient, and the Joint Information Uncertainty (Bonham-Carter, 1994). As a result of these tests, one of the correlated variables can be either eliminated or combined with the second to form a new variable that will replace both in the integrated model. The two former methods are based on the chi-square statistic while the latter is derived from the Joint Entropy measure; all methods are calculated from a contingency table
+The correlation between each pair of variables is calculated from a contingency table built by cross-tabulating the two maps, using Cramer's coefficient and the joint entropy method, following Bonham-Carter (1994).
-produced by cross-tabulating pair of maps.
-==== References ====
+Reports an error if Transition is empty.
-Bonham-Carter, G 1994. Geographic information systems for geoscientists: modelling with GIS. New York, Pergamon.
+Reports an error if a spatial variable named in Ranges is not provided by a nested Name Map hook.
-===== Internal Name =====
+**References**
+Bonham-Carter, G., 1994. Geographic information systems for geoscientists: modelling with GIS. New York, Pergamon.
+===== Internal Name =====
 DetermineWeightsOfEvidenceCorrelation
+===== Usage examples =====
+See practical examples of this functor in [[lesson_18|Lesson 18: Building a land-use and land-cover change simulation model]]