Multivariate interpolation

Multivariate interpolation is a way to use two or more pieces of data to find a third value that lies in between them. Imagine looking at a map of a town on paper. You know the population of two different neighborhoods, let's say 3,000 people and 5,000 people. If you wanted to estimate the population of the part of town that lies between those two neighborhoods, you would use multivariate interpolation to find out. It could tell you that this part of town has about 4,000 people living there.