A projection of data from the apex of a cone in a three-dimensional plot onto a surface at the base of the cone. This projection often is performed in log analysis to remove a dimension and see what a data point would read in the absence of that dimension. For example, removal of shale effects in a plot of neutron, density and gamma ray data helps determine the mineralogy of a sample where the apex of the cone would represent the shale point in the plot.
The M-N plot is a plot in which the fluid has been removed by conical projection from the neutron, density and sonic data to provide a porosity-independent plot that can be used to determine lithology.