Description: Aimed at scientists, engineers, modelers and other technical users of GIS/mapping applications, this lesson provides a basic understanding of different vertical datums, how they are defined, some of their strengths and weaknesses and how to choose the appropriate datum for a given application. The lesson starts with basic definitions of height and vertical datums and guidance on choosing and working with the appropriate datum for a given situation. It then provides a conceptual introduction to ellipsoidal, geopotential and tidal datums including appropriate uses, examples and pros and cons.