From the Vega Example Gallery
Pie charts encode proportional differences among a set of numeric values as the angular extent and in area of a circular slice.
Similarly 'doughnut charts' encode proportional differences but with a central 'hole' to reduce emphasis on variability in area saliency.
This radial plot uses both angular and radial extent to convey multiple dimensions of data. However, this approach is not perceptually effective, as viewers will most likely be drawn to the total area of the shape, conflating the two dimensions. This example also demonstrates one way to add labels to circular plots.
A radar chart displaya multivariate data in the form of a two-dimensional radual layout of three or more quantitative variables whose magnitude is represented by distsance from a central point. Useful for quantitative variables that have a circular distribution (e.g. temporal cycles and azimuthal directions).