Determine plotting order of features — tm_plot

Determine plotting order of features.

Usage

tm_plot_order(
  aes,
  reverse = TRUE,
  na.order = c("mix", "bottom", "top"),
  null.order = c("bottom", "mix", "top"),
  null.below.na = TRUE
)

aes: Visual variable for which the values determine the plotting order. Example: bubble map where the "size" aesthetic is used. A data variable (say population) is mapped via a continuous scale (tm_scale_continuous()) to bubble sizes. The bubbles are plotted in order of size. How is determined by the other arguments. Use "DATA" to keep the same order as in the data. Another special value are "AREA" and "LENGTH" which are preserved for polygons and lines respectively: rather than a data variable the polygon area / line lengths determines the plotting order.
reverse: Logical that determines whether the visual values are plotted in reversed order. The visual values (specified with tmap option "values.var") are by default reversed, so plotted starting from the last value. In the bubble map example, this means that large bubbles are plotted first, hence at the bottom.
na.order: Where should features be plotted that have an NA value for (at least) one other aesthetic variable? In the (order) "mix", at the "bottom", or on "top"? In the bubble map example: if fill color is missing for some bubble, where should those bubbles be plotted?
null.order: Where should non-selected (aka null) features be plotted?
null.below.na: Should null features be plotted below NA features?