This data set contains measurements of calcium content 
in a 0-20 cm soil layer

The columns corresponds to 
 1. leste   	: x-coordinate      
 2. norte   	: y-coordinate
 3. altitude	: altitude 
 4. area    	: code of area classification (1-3) 
 5. ca20	: calcuim content in a 0-20cm soil layer

