examples/tm_add_legend.R

In mtennekes/tmap: Thematic Maps

# This example adds a manual legend that combines the tm_symbols color and size legend.
\dontrun{
data(World)
data(metro)

# legend bubble size (10, 20, 30, 40 million) are
# - are normlized by upper limit (40e6),
# - square rooted (see argument perceptual of tm_symbols), and 
# - scaled by 2:
bubble_sizes <- ((c(10, 20, 30, 40) * 1e6) / 40e6) ^ 0.5 * 2 

tm_shape(World) + 
	tm_polygons() + 
tm_shape(metro) +
	tm_symbols(col='pop2020', 
		breaks = c(0, 15, 25, 35, 40) * 1e6,
		n=4,
		palette = 'YlOrRd',
		size='pop2020',
		sizes.legend = c(10, 20, 30, 40) * 1e6,
		size.lim = c(0, 40e6),
		scale = 2,
		legend.size.show = FALSE,    # comment this line to see the original size legend
		legend.col.show = FALSE,     # comment this line to see the original color legend
		legend.size.is.portrait = TRUE) + 
tm_add_legend('symbol', 
	col = RColorBrewer::brewer.pal(4, "YlOrRd"),
	border.col = "grey40",
	size = bubble_sizes,
	labels = c('0-15 mln','15-25 mln','25-35 mln','35-40 mln'),
	title="Population Estimate")
}

# See also the documentation of tm_symbols for another example