Map layer: polygons

Map layer that draws polygons. Supported visual variables are: fill (the fill color), col (the border color), lwd (line width), lty (line type), fill_alpha (fill color alpha transparency) and col_alpha (border color alpha transparency).

Usage

tm_polygons(
  fill = tm_const(),
  fill.scale = tm_scale(),
  fill.legend = tm_legend(),
  fill.chart = tm_chart_none(),
  fill.free = NA,
  col = tm_const(),
  col.scale = tm_scale(),
  col.legend = tm_legend(),
  col.chart = tm_chart_none(),
  col.free = NA,
  lwd = tm_const(),
  lwd.scale = tm_scale(),
  lwd.legend = tm_legend(),
  lwd.chart = tm_chart_none(),
  lwd.free = NA,
  lty = tm_const(),
  lty.scale = tm_scale(),
  lty.legend = tm_legend(),
  lty.chart = tm_chart_none(),
  lty.free = NA,
  fill_alpha = tm_const(),
  fill_alpha.scale = tm_scale(),
  fill_alpha.legend = tm_legend(),
  fill_alpha.chart = tm_chart_none(),
  fill_alpha.free = NA,
  col_alpha = tm_const(),
  col_alpha.scale = tm_scale(),
  col_alpha.legend = tm_legend(),
  col_alpha.chart = tm_chart_none(),
  col_alpha.free = NA,
  linejoin = "round",
  lineend = "round",
  plot.order = tm_plot_order("lwd", reverse = TRUE, na.order = "bottom"),
  zindex = NA,
  group = NA,
  group.control = "check",
  popup = tm_popup(),
  popup.vars = NA,
  popup.format = tm_label_format(),
  hover = NA,
  id = "",
  blend = "over",
  options = opt_tm_polygons(),
  ...
)

tm_fill(...)

tm_borders(col = tm_const(), ...)

opt_tm_polygons(polygons.only = "ifany")

Arguments

fill, fill.scale, fill.legend, fill.chart, fill.free

Visual variable that determines the fill color. See details. Unit: Color – a color name, hex string, or (when mapped) a palette name.

col, col.scale, col.legend, col.chart, col.free

Visual variable that determines the color. See details. Unit: Color – a color name, hex string, or (when mapped) a palette name.

lwd, lwd.scale, lwd.legend, lwd.chart, lwd.free

Visual variable that determines the line width. See details. Unit: Base R line-width units; 1 lwd is approx. 0.75 pt at 96 dpi. Controlled by values.scale.

lty, lty.scale, lty.legend, lty.chart, lty.free

Visual variable that determines the line type. See details. Unit: Integer (1-6) or name: "solid", "dashed", "dotted", "dotdash", "longdash", "twodash".

fill_alpha, fill_alpha.scale, fill_alpha.chart, fill_alpha.legend, fill_alpha.free

Visual variable that determines the fill color transparency. See details. Unit: Proportion – numeric 0-1 (0 = fully transparent, 1 = fully opaque).

col_alpha, col_alpha.scale, col_alpha.legend, col_alpha.chart, col_alpha.free

Visual variable that determines the color transparency. See details. Unit: Proportion – numeric 0-1 (0 = fully transparent, 1 = fully opaque).

linejoin, lineend

Line join and line end. See gpar() for details.

plot.order

Specification in which order the spatial features are drawn. See tm_plot_order() for details.

zindex

Controls the stacking order of map layers. Should be set to a value above 400. By default, layers are stacked in call order, starting at 401. See details.

group

Name of the group to which this layer belongs. This is only relevant in view mode, where layer groups can be switched (see group.control)

group.control

In view mode, the group control determines how layer groups can be switched on and off. Options: "radio" for radio buttons (meaning only one group can be shown), "check" for check boxes (so multiple groups can be shown), and "none" for no control (the group cannot be (de)selected).

popup

popup specification for "view" mode, the output of tm_popup(). It determines the data variables shown in the popup table, the popup title, and (in the future) the popup layout. This replaces the deprecated arguments popup.vars and popup.format.

popup.vars

(Deprecated.) Use popup with tm_popup() instead (via its vars argument). Names of data variables that are shown in the popups in "view" mode. Set popup.vars to TRUE to show all variables in the shape object. Set popup.vars to FALSE to disable popups. Set popup.vars to a character vector of variable names to show those variables in the popups. The default (NA) depends on whether visual variables (e.g. fill) are used. If so, only those are shown. If not, all variables in the shape object are shown.

popup.format

(Deprecated.) Use popup with tm_popup() instead (via its format argument). List of formatting options for the popup values. Output of tm_label_format(). Only applicable for numeric data variables. If one list of formatting options is provided, it is applied to all numeric variables of popup.vars. Also, a (named) list of lists can be provided. In that case, each list of formatting options is applied to the named variable.

hover

name of the data variable that specifies the hover labels (view mode only). Set to FALSE to disable hover labels. By default FALSE, unless id is specified. In that case, it is set to id,

id

name of the data variable that specifies the indices of the spatial features. Only used for "view" mode.

blend

Compositing operator for layer blending. Default "over" applies no blending. See the "Layer blending" section for the supported values.

options

options passed on to the corresponding opt_<layer_function> function

...

to catch deprecated arguments from version < 4.0

polygons.only

should only polygon geometries of the shape object (defined in tm_shape()) be plotted? By default "ifany", which means TRUE in case a geometry collection is specified.

Details

The visual variable arguments (e.g. col) can be specified with a data variable name (e.g., a spatial vector attribute or a raster layer of the object specified in tm_shape()), with a visual value (for col, a color is expected), or with a geometry-derived variable (see below). See vignette about visual variables.

Multiple values can be specified: in that case facets are created. These facets can be combined with other faceting data variables, specified with tm_facets(). See vignette about facets.

• The *.scale arguments determine the used scale to map the data values to visual variable values. These can be specified with one of the available tm_scale_*() functions. The default is specified by the tmap option (tm_options()) scales.var. See vignette about scales.

• The *.legend arguments determine the used legend, specified with tm_legend(). The default legend and its settings are determined by the tmap options (tm_options()) legend. . See vignette about legends.

• The *.chart arguments specify additional charts, specified with tm_chart_, e.g. tm_chart_histogram(). See vignette about charts.

• The *.free arguments determine whether scales are applied freely across facets, or shared. A logical value is required. They can also be specified with a vector of three logical values; these determine whether scales are applied freely per facet dimension. This is only useful when facets are applied (see tm_facets()). There are maximally three facet dimensions: rows, columns, and pages. This only applies for a facet grid (tm_facets_grid()). For instance, col.free = c(TRUE, FALSE, FALSE) means that for the visual variable col, each row of facets will have its own scale, and therefore its own legend. For facet wraps and stacks (tm_facets_wrap() and tm_facets_stack()) there is only one facet dimension, so the *.free argument requires only one logical value.

Currently, three geometry-derived variables are implemented:

• "AREA" (polygons only), which uses the feature area;

• "LENGTH" (lines only), which uses the feature length; and

• "MAP_COLORS", which assigns values so that adjacent features receive different values, making it particularly suitable for coloring neighbouring polygons.

Note that geometry-derived variables do not generate a legend automatically. If a legend is required, compute the corresponding variable explicitly, for example with sf::st_area(), sf::st_length(), or tmaptools::map_coloring(), and use the resulting values instead.

Visual variable units

Every visual variable maps data values to a specific output unit. Knowing the unit matters when supplying constant values via tm_const(), or output ranges via values.range / values.scale in the scale functions.

Variable	Output unit	Notes
fill, col, bgcol	color	name, hex, or palette string
fill_alpha, col_alpha, bgcol_alpha	proportion 0-1	0 = transparent, 1 = opaque
size (symbols, bubbles, squares, dots)	typographic lines	1 line approx. 1/6 inch; scaled by values.scale
size (circles)	meters	plain numeric or a units object
size (text, labels)	multiplier	1 = 12 pt (plot) / 12 px (view)
lwd	lwd	base R units; 1 lwd approx. 0.75 pt at 96 dpi
lty	–	integer 1-6 or name ("solid", "dashed", ...)
shape	–	integer pch 1-25 or single character
angle	degrees	0-360, clockwise from north
fontface	–	"plain", "bold", "italic", "bold.italic"

Symbol size (size in tm_symbols, tm_bubbles, tm_squares, tm_dots)

"Lines" is a typographic unit: one line is approximately 1/6 inch (the default base line-height in R graphics). The global multiplier tmap_options(values.scale = list(size.bubbles = 1.5)) scales all symbol sizes without changing the data mapping.

Circle size (size in tm_circles)

The value is a geographic radius in meters. A plain numeric vector is interpreted as meters; a units object (from the units package) is automatically converted, so units::as_units(1, "mi") gives a 1-mile radius. Because the radius is geographic, circles scale with zoom in interactive (view) mode – unlike bubble symbols which keep a fixed screen size.

Text size (size in tm_text, tm_labels)

The value is a multiplier of the base font size. size = 1 renders at 12 pt in plot mode (R's default par("ps")) and at 12 px in view mode (gp$cex * 12 px, see tmapLeafletDataPlot.tm_data_text); the two modes are consistent by design.

Layer blending (blend)

Blend modes control how a layer's pixels are combined with the pixels beneath it. For each pixel, let \(S\) be the source (top layer) RGB value and \(D\) be the destination (bottom layer) RGB value, both normalised to \([0, 1]\).

blend	Formula	Use case
"over"	\(S \cdot \alpha + D \cdot (1 - \alpha)\)	Standard alpha compositing (default)
"multiply"	\(S \times D\)	Hillshading over colour raster; both layers darken each other
"screen"	\(1 - (1 - S)(1 - D)\)	Inverse of multiply; brightens
"overlay"	multiply if \(D < 0.5\), screen if \(D \geq 0.5\)	Boosts contrast; preserves midtones
"darken"	\(\min(S, D)\)	Keeps the darker of the two layers per channel
"lighten"	\(\max(S, D)\)	Keeps the lighter of the two layers per channel

Requires R >= 4.2 and a compatible graphics device (e.g. png(type = "cairo"), svg()). In view mode, blending is applied via CSS mix-blend-mode. See grid::groupGrob() for the full list of supported operators.

zindex and pane names

In view mode, each layer is rendered in a Leaflet pane named "tmap{zindex}" (e.g., "tmap401", "tmap402"), with base tile layers placed in the standard "tile" pane.

See also

Choropleth example (1) and choropleth example (2)

Examples

# load Africa country data
data(World)
Africa = World[World$continent == "Africa", ]
Africa_border = sf::st_make_valid(sf::st_union(sf::st_buffer(Africa, 0.001))) # slow and ugly

# without specifications
tm_shape(Africa_border) + tm_polygons()

tm_shape(Africa_border) + tm_fill()

tm_shape(Africa_border) + tm_borders()


# specification with visual variable values
tm_shape(Africa) +
  tm_polygons(fill = "limegreen", col = "purple", lwd = 2, lty = "solid", col_alpha = 0.3) +
  tm_text("name", options = opt_tm_text(remove_overlap = TRUE)) +
tm_shape(Africa_border) +
  tm_borders("darkred", lwd = 3)


# specification with a data variable
tm_shape(Africa) +
  tm_polygons(fill = "income_grp", fill.scale = tm_scale_categorical(values = "-tol.muted"))



# continuous color scale with landscape legend
tm_shape(Africa) +
  tm_polygons(fill = "inequality",
    fill.scale = tm_scale_continuous(values = "-scico.roma"),
    fill.legend = tm_legend(
      title = "", orientation = "landscape",
      position = tm_pos_out("center", "bottom"), frame = FALSE
      )) +
tm_shape(Africa_border) +
  tm_borders(lwd = 2) +
tm_title("Inequality index", position = tm_pos_in("right", "TOP"), frame = FALSE) +
tm_layout(frame = FALSE)


# bivariate scale
tm_shape(World) +
  tm_polygons(tm_vars(c("inequality", "well_being"), multivariate = TRUE))
#> bivariate legend Labels abbreviated by the first two letters, e.g.: "2.0 - 2.9"
#> => "2".
#> This message is displayed once per session.