Correlation, Method of Least Squares, Linear Regression and the General Linear Model - Geomathematics: Theoretical Foundations, Applications and Future Developments - page 120

Fig. 4.4 Distribution of copper deposits in area outlined in Fig. 4.3 ; deposits with more than
1,000 t of copper are circled .(a) East-central Ontario; (b) Western Quebec. Alternate lines
(8 miles apart) are shown for grid to be used for harmonic analysis in Chap. 7 (Source: Agterberg
1974 , Fig. 80)
combinations of features co-occurring in the same cells, 45 additional explanatory
variables were formed that are cross-products of the preceding 10 attributes. As is
usual in applications of multiple regression, a dummy variable with value equal to 1
in all cells was added to obtain 56 explanatory variables in total.