Scales in tmap are configured by the family of functions with prefix tm_scale.
Such function should be used for the input of the .scale arguments in the
layer functions (e.g. fill.scale in tm_polygons()). The function tm_scale()
is a scale that is set automatically given by the data type (factor, numeric, and integer)
and the visual variable. The tmap option scales.var contains information
which scale is applied when.
tm_scale(...)arguments passed on to the applied scale function tm_scale_*()
tm_scale_asis(), tm_scale_ordinal(), tm_scale_categorical(),
tm_scale_intervals(), tm_scale_discrete(), tm_scale_continuous(),
tm_scale_rank(), tm_scale_continuous_log(), tm_scale_continuous_log2(),
tm_scale_continuous_log10(), tm_scale_continuous_log1p(), tm_scale_continuous_sqrt(),
tm_scale_continuous_pseudo_log(), tm_scale_rgb(), tm_scale_bivariate()