A mechanism is provided for making a discrete spatial correlation on a 2D grid continuous. The region has given grid points and each of the grid points has its discrete stochastic variable. Additional grid points and associated stochastic variables are established on the boundary and corners of the region. All correlation coefficients are obtained among the given discrete stochastic variables and the additional discrete stochastic variables. For each of two given spatial points whose spatial correlation is needed, a quadrilateral containing it is identified by four grid points, and a stochastic variable for it is expressed as a weighted linear combination of four stochastic variables at four grid points, with four weights being a continuous function of the coordinate of the point. The resulting spatial correlation is a weighted linear combination of multiple discrete correlation coefficients each weight being a continuous function of the coordinates of the two given points.