Inset Plots for Spatial Data Visualization

Tools for easily and flexibly creating 'ggplot2' maps with inset maps. One crucial feature of maps is that they have fixed coordinate ratios, i.e., they cannot be distorted, which makes it difficult to manually place inset maps. This package provides functions to automatically position inset maps based on user-defined parameters, making it extremely easy to create maps with inset maps with minimal code.

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