Coordinate systems for evoked potential topography

Two coordinate systems for specifying the position of a point on the scalp are described. The coordinates resemble those of conventional cartography, but are related to irregular solids by using proportional curvilinear surface units instead of solid angular geometry. Cylindrical projections convert the coordinate lines into rectangular graticules for isopotential maps of sensory evoked responses. Visual and somatosensory data are presented to illustrate the techniques. The practical advantages of these principles applied to contemporary developments in colour contour displays are discussed.