The variables are:
East |
a code for east-west direction |
North |
a code for north-south direction |
Cressie, N. (1993). Statistics for Spatial Data, revised edition. New York: Wiley. Gomez, M. and Hazen, K. (1970). Evaluating sulfur and ash distribution in coal seams by statistical response surface regression analysis. Report RI 7377, U.S. Bureau of Mines, Washington, D. C.