Blasius, Jörg; Eilers, Paul H. C. and Gower, John Computational
Statistics and Data Analysis, 53(8), (Click here to request a
copy from the OU Author. The elements of a biplot are (i) a set
of axes representing variables, usually concurrent at the
centroid of (ii) a set of points representing samples or cases.
The axes are (approximations to) conventional coordinate axes,
and therefore may be labelled and calibrated. Especially when
there are many points (perhaps several thousand) the whole
effect can be very confusing but this may be mitigated by: 1.
Giving a density representation of the points. 2. While
respecting the calibrations, moving the axes to new positions
more remote from the points, and possibly jointly rotating axes
and points. 3. The use of colour — when permissible. 4. Choosing
more than one centre of concurrency. The principles are quite
general but we illustrate them by examples of the Categorical
Principal Component Analysis of the responses to questions
concerning migration in Germany. Thi