Inset Plots for Spatial Data Visualization.

insetplot

insetplot is an R package to create ggplot2 maps with inset maps easily and flexibly. It handles spatial configuration, aspect ratios, and plot composition automatically.

Quick start

Approach 1: Reuse one plot (simplest)

Use the same plot for the main map and all insets — let insetplot handle sizing and positioning.

library(insetplot)
library(sf)
library(ggplot2)

# Load data
nc <- st_read(system.file("shape/nc.shp", package = "sf"), quiet = TRUE)

# Configure insets: one main + one inset
config_insetmap(
  bbox = st_bbox(nc),
  specs = list(
    inset_spec(main = TRUE),
    inset_spec(
      xmin = -84, xmax = -75, ymin = 33, ymax = 37,
      loc = "left bottom", scale_factor = 0.5
    )
  )
)

# Compose
with_inset(
  ggplot(nc, aes(fill = AREA)) +
    geom_sf() +
    scale_fill_viridis_c() +
    theme_void()
)

Approach 2: Custom plot per subplot

Provide specific plots for the main and inset maps.

base_plot <- ggplot(nc, aes(fill = AREA)) +
  geom_sf() + scale_fill_viridis_c() + theme_void()

main_plot <- base_plot +
  ggtitle("Full North Carolina") 

inset_plot <- base_plot +
  ggtitle("Detail Region") 

config_insetmap(
  bbox = st_bbox(nc),
  specs = list(
    inset_spec(main = TRUE, plot = main_plot),
    inset_spec(
      xmin = -84, xmax = -75, ymin = 33, ymax = 37,
      loc = "left bottom", scale_factor = 0.5,
      plot = inset_plot
    )
  )
)

with_inset()  # plot argument optional when each spec has its own plot

Installation

To install the released version from CRAN:

install.packages("insetplot")

To install the development version from GitHub:

devtools::install_github("fncokg/insetplot")

Documentation

Full documentation and more examples are available at insetplot package site.

Fast overview of main functions

• inset_spec() — Define bbox, position, and size for each subplot

  • bbox: xmin, xmax, ymin, ymax
  • position: loc (e.g., "left bottom") or loc_left/loc_bottom in [0, 1]
  • size: prefer scale_factor; or provide one of width/height
  • plot: optional custom ggplot object
  • main: exactly one spec must set main = TRUE

• config_insetmap() — Build and store configuration

  • specs: list of inset_spec(), required
  • bbox: overall bounding box (sf bbox or similar), optional (all specs must have fullly defined bboxes if omitted)
  • to_crs: target Coordinate Reference System, optional, by default "EPSG:4326"
  • from_crs: source CRS for non-sf inputs, optional, by default "EPSG:4326"
  • border_args: forwarded to map_border() for inset borders, optional

• with_inset() — Compose main plot with insets

  • plot: single ggplot or list per spec
  • .as_is: return the input plot as-is (skip inset composition)
  • .return_details: return list(full, subplots, subplot_layouts, main_ratio)

• ggsave_inset() — Save with the correct aspect ratio

  • Provide one of width or height; the other is computed from main_ratio
  • Optional ratio_scale for small adjustments (e.g., legends)

• map_border() — Small theme to draw a rectangular border around plots

Further examples

Custom positioning and sizing

config_insetmap(
  bbox = st_bbox(nc),
  specs = list(
    inset_spec(main = TRUE),
    inset_spec(
      xmin = -84, xmax = -75, ymin = 33, ymax = 37,
      loc_left = 0.05, loc_bottom = 0.05,
      # Use width only; height auto-calculated to preserve aspect ratio
      width = 0.25
    )
  )
)

with_inset(base_plot)

Pass custom plots after configuration

config_insetmap(
  bbox = st_bbox(nc),
  specs = list(
    inset_spec(main = TRUE),
    inset_spec(
      xmin = -84, xmax = -75, ymin = 33, ymax = 37,
      loc = "left bottom", scale_factor = 0.5,
    )
  )
)

with_inset(list(main_plot, inset_plot))

Save with correct aspect ratio

ggsave_inset(
  "map_with_insets.png",
  # `height` auto-calculated from `main_ratio`
  width = 12,
  dpi = 300
)

Debugging with detailed output

result <- with_inset(plot = my_plot, .return_details = TRUE)
# result$full, result$subplots, result$subplot_layouts, result$main_ratio