Spatial interpolation
If spatial sampling is an efficient way of capturing knowledge of spatial variation, then there must be reliable ways of filling in the unknown variation between sample points. Spatial interpolation attempts to do this, by providing a method of estimating the value of a field anywhere from a limited number of sample points. 
Many methods of spatial interpolation exist, all of them based to some extent on the principle that conditions vary smoothly over the Earth’s surface. The most rigorous approach to interpolation is Kriging, a family of techniques based on the theory of geostatistics (Isaaks and Srivastava, 1989). 
