  The nature of the radio-wave radiation generated by particle cascades in both
the Earth's atmosphere and dense media such as ice has, historically, been much
debated. This situation changed in the early 2010's, with the community
converging on the common terminology of "geomagnetic" and "Askaryan" radiation
to describe the two emission mechanisms. However, this convergence arose from
discussions at various conferences and workshops, and was ultimately reached
through agreement between simulation codes and experimental measurements. In
this article therefore, I use relatively simple geometrical arguments, and a
minimum of calculations based on single particle tracks, to explain the nature
of radiation from extensive air showers (EAS) and cascades in dense media such
as ice. I identify well-determined frequency regimes where the radiation from
the Askaryan effect will be bremsstrahlung-like and Cherenkov-like, being
respectively below/above 1 GHz in EAS and 100 MHz in dense media; and where
geomagnetic emission will be transverse-current-like and where it will resemble
synchrotron radiation, respectively below/above a few GHz in EAS, depending on
the height of cascade development. I suggest how these transitions in the
nature of the emission may be experimentally observed.
