Map coloring

Color the polygons of a map such that adjacent polygons have different colors

Usage

map_coloring(
  x,
  algorithm = "greedy",
  ncols = NA,
  minimize = FALSE,
  palette = NULL,
  contrast = 1
)

Arguments

x

Either a shape (i.e. a sf or SpatialPolygons(DataFrame) (sp package) object), or an adjacency list.

algorithm

currently, only "greedy" is implemented.

ncols

number of colors. By default it is 8 when palette is undefined. Else, it is set to the length of palette

minimize

logical that determines whether algorithm will search for a minimal number of colors. If FALSE, the ncols colors will be picked by a random procedure.

palette

color palette.

contrast

vector of two numbers that determine the range that is used for sequential and diverging palettes (applicable when auto.palette.mapping=TRUE). Both numbers should be between 0 and 1. The first number determines where the palette begins, and the second number where it ends. For sequential palettes, 0 means the brightest color, and 1 the darkest color. For diverging palettes, 0 means the middle color, and 1 both extremes. If only one number is provided, this number is interpreted as the endpoint (with 0 taken as the start).

Value

If palette is defined, a vector of colors is returned, otherwise a vector of color indices.

Examples

if (require(tmap) && packageVersion("tmap") >= "3.99") {
    data(World, metro)

    World$color <- map_coloring(World, palette="Pastel2")
    qtm(World, fill = "color")

    # map_coloring used indirectly: qtm(World, fill = "MAP_COLORS")

    data(NLD_prov, NLD_muni)
    tm_shape(NLD_prov) +
      tm_fill("name",
              fill.legend = tm_legend_hide()) +
    tm_shape(NLD_muni) +
      tm_polygons("MAP_COLORS",
                  fill_alpha = .25,
                  fill.scale = tm_scale(values = "brewer.greys")) +
    tm_shape(NLD_prov) +
      tm_borders(lwd=2) +
      tm_text("name", options = opt_tm_text(shadow = TRUE)) +
    tm_title("Dutch provinces and\nmunicipalities", bg.color="white")
}