Am I misunderstanding the scipy.interpolate.interp2d docs? It says that anything outside the domain returns nan by default. When I try 5.0, 5.0, clearly outside of the domain it returns the value of the nearest point, which is 4.0. >>> interpolate.interp2d([1,1,2,2.0], [1,2,1,2.0], [1,2,3,4.0])(5.0,5.0) array([ 4.]) --Tom