A radar puts its categories around a circle rather than along an axis, and MAIDR reads it as a multi-line layer: each spoke is a column, each series a row. What the circle adds is where a spoke sits — the stereo position follows the spoke's angle instead of its index, so sweeping the spokes goes out and comes back.
A polar area (coxcomb, rose) draws the same values as wedges instead of an outline. It is read identically; only the mark differs.