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Add legends to Mapbox GL and MapLibre GL maps

Source: R/legends.R
map_legends.Rd

These functions add categorical and continuous legends to maps. Use legend_style() to customize appearance and clear_legend() to remove legends.

Usage

add_legend(
  map,
  legend_title,
  values,
  colors,
  type = c("continuous", "categorical"),
  circular_patches = FALSE,
  patch_shape = "square",
  position = "top-left",
  sizes = NULL,
  add = FALSE,
  unique_id = NULL,
  width = NULL,
  layer_id = NULL,
  margin_top = NULL,
  margin_right = NULL,
  margin_bottom = NULL,
  margin_left = NULL,
  style = NULL
)

add_categorical_legend(
  map,
  legend_title,
  values,
  colors,
  circular_patches = FALSE,
  patch_shape = "square",
  position = "top-left",
  unique_id = NULL,
  sizes = NULL,
  add = FALSE,
  width = NULL,
  layer_id = NULL,
  margin_top = NULL,
  margin_right = NULL,
  margin_bottom = NULL,
  margin_left = NULL,
  style = NULL
)

add_continuous_legend(
  map,
  legend_title,
  values,
  colors,
  position = "top-left",
  unique_id = NULL,
  add = FALSE,
  width = NULL,
  layer_id = NULL,
  margin_top = NULL,
  margin_right = NULL,
  margin_bottom = NULL,
  margin_left = NULL,
  style = NULL
)

Arguments

map

A map object created by the mapboxgl or maplibre function.

legend_title

The title of the legend.

values

The values being represented on the map (either a vector of categories or a vector of stops).

colors

The corresponding colors for the values (either a vector of colors, a single color, or an interpolate function).

type

One of "continuous" or "categorical" (for add_legend only).

circular_patches

(Deprecated) Logical, whether to use circular patches in the legend. Use patch_shape = "circle" instead.

patch_shape

Character or sf object, the shape of patches to use in categorical legends. Can be one of the built-in shapes ("square", "circle", "line", "hexagon"), a custom SVG string (e.g., ''), or an sf object with POLYGON or MULTIPOLYGON geometry (which will be automatically converted to SVG). Default is "square".

position

The position of the legend on the map (one of "top-left", "bottom-left", "top-right", "bottom-right").

sizes

An optional numeric vector of sizes for the legend patches, or a single numeric value (only for categorical legends). For line patches, this controls the line thickness.

add

Logical, whether to add this legend to existing legends (TRUE) or replace existing legends (FALSE). Default is FALSE.

unique_id

Optional. A unique identifier for the legend. If not provided, a random ID will be generated.

width

The width of the legend. Can be specified in pixels (e.g., "250px") or as "auto". Default is NULL, which uses the built-in default.

layer_id

The ID of the layer that this legend is associated with. If provided, the legend will be shown/hidden when the layer visibility is toggled.

margin_top

Custom top margin in pixels, allowing for fine control over legend positioning. Default is NULL (uses standard positioning).

margin_right

Custom right margin in pixels. Default is NULL.

margin_bottom

Custom bottom margin in pixels. Default is NULL.

margin_left

Custom left margin in pixels. Default is NULL.

style

Optional styling options created by legend_style() or a list of style options.

Value

The updated map object with the legend added.

Examples

if (FALSE) { # \dontrun{
# Basic categorical legend
add_legend(map, "Population",
          values = c("Low", "Medium", "High"),
          colors = c("blue", "yellow", "red"),
          type = "categorical")

# Continuous legend with custom styling
add_legend(map, "Income",
          values = c(0, 50000, 100000),
          colors = c("blue", "yellow", "red"),
          type = "continuous",
          style = list(
            background_color = "white",
            background_opacity = 0.9,
            border_width = 2,
            border_color = "navy",
            text_color = "darkblue",
            font_family = "Times New Roman",
            title_font_weight = "bold"
          ))

# Legend with custom styling using a list
add_legend(map, "Temperature",
          values = c(0, 50, 100),
          colors = c("blue", "yellow", "red"),
          type = "continuous",
          style = list(
            background_color = "#f0f0f0",
            title_size = 16,
            text_size = 12,
            shadow = TRUE,
            shadow_color = "rgba(0,0,0,0.1)",
            shadow_size = 8
          ))

# Dark legend with white element borders
add_legend(map, "Elevation",
          values = c(0, 1000, 2000, 3000),
          colors = c("#2c7bb6", "#abd9e9", "#fdae61", "#d7191c"),
          type = "continuous",
          style = list(
            background_color = "#2c3e50",
            text_color = "white",
            title_color = "white",
            element_border_color = "white",
            element_border_width = 1
          ))

# Categorical legend with circular patches
add_categorical_legend(
    map = map,
    legend_title = "Population",
    values = c("Low", "Medium", "High"),
    colors = c("#FED976", "#FEB24C", "#FD8D3C"),
    patch_shape = "circle",
    sizes = c(10, 15, 20),
    style = list(
      background_opacity = 0.95,
      border_width = 1,
      border_color = "gray",
      title_color = "navy",
      element_border_color = "black",
      element_border_width = 1
    )
)

# Legend with line patches for line layers
add_categorical_legend(
    map = map,
    legend_title = "Road Type",
    values = c("Highway", "Primary", "Secondary"),
    colors = c("#000000", "#333333", "#666666"),
    patch_shape = "line",
    sizes = c(5, 3, 1)  # Line thickness in pixels
)

# Legend with hexagon patches (e.g., for H3 data)
add_categorical_legend(
    map = map,
    legend_title = "H3 Hexagon Categories",
    values = c("Urban", "Suburban", "Rural"),
    colors = c("#8B0000", "#FF6347", "#90EE90"),
    patch_shape = "hexagon",
    sizes = 25
)

# Custom SVG shapes - triangle
add_categorical_legend(
    map = map,
    legend_title = "Mountain Peaks",
    values = c("High", "Medium", "Low"),
    colors = c("#8B4513", "#CD853F", "#F4A460"),
    patch_shape = '<polygon points="50,10 90,90 10,90" />'
)

# Custom SVG shapes - star
add_categorical_legend(
    map = map,
    legend_title = "Ratings",
    values = c("5 Star", "4 Star", "3 Star"),
    colors = c("#FFD700", "#FFA500", "#FF6347"),
    patch_shape = '<path d="M50,5 L61,35 L95,35 L68,57 L79,91 L50,70 L21,91 L32,57 L5,35 L39,35 Z" />'
)

# Custom SVG with complete SVG string
add_categorical_legend(
    map = map,
    legend_title = "Custom Icons",
    values = c("Location A", "Location B"),
    colors = c("#FF0000", "#0000FF"),
    patch_shape = '<svg viewBox="0 0 100 100"><circle cx="50" cy="50" r="40" stroke="black" stroke-width="3" /></svg>'
)

# Using sf objects directly as patch shapes
library(sf)
nc <- st_read(system.file("shape/nc.shp", package = "sf"))
county_shape <- nc[1, ]  # Get first county

add_categorical_legend(
    map = map,
    legend_title = "County Types",
    values = c("Rural", "Urban", "Suburban"),
    colors = c("#228B22", "#8B0000", "#FFD700"),
    patch_shape = county_shape  # sf object automatically converted to SVG
)

# For advanced users needing custom conversion options
custom_svg <- mapgl:::.sf_to_svg(county_shape, simplify = TRUE, tolerance = 0.001, fit_viewbox = TRUE)
add_categorical_legend(
    map = map,
    legend_title = "Custom Converted Shape",
    values = c("Type A"),
    colors = c("#4169E1"),
    patch_shape = custom_svg
)

} # }