Spatial interpolation is the process of estimating an unknown value between two known values taking into account Tobler's First Law:
"Everything is related to everything else, but near things are more related than distant things."
This recipe does not undertake to teach you the advanced concept of interpolation because it is too complex for this book. Instead, this recipe will guide you to create a terrain surface using the following:
Note
For further research, please refer to: Geographic Information Analysis, David O'Sullivan and David Unwin, John Wiley & Sons, Inc., 2003, specifically the 8.3 Spatial interpolation recipe of Chapter 8, Describing and Analyzing Fields, pp.220-234.