This lecture introduces the concept of spatial interpolation in the context of geographic information systems. It covers topics such as global and local deterministic interpolation methods, including regression, nearest neighbor, B-spline, and weighted moving average. The lecture explains the differences between global and local methods, the importance of expert knowledge in selecting the appropriate method, and the potential errors associated with deterministic methods. It also discusses techniques for cross-validation to estimate uncertainty and concludes by highlighting the arbitrary nature of method selection and the resulting uncertainty in the interpolation process.