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.
See also
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()