ggplot and label: How to shift the text outside?

Overview of the Problem

In this article, we will explore how to create a map with geographical data using R and the popular ggplot package. Specifically, we will focus on shifting the text labels (city names) outside their corresponding borders.

Introduction to ggplot and sf Packages

To tackle this problem, we first need to understand the basics of ggplot and its integration with the sf package. The sf package provides a convenient interface for working with spatial data in R.

The sf (Simple Features) package is an implementation of the OGC Simple Features Specification in R. It allows you to easily create, manipulate, and analyze geographic data. In this example, we will use sf to create a simple polygon representing our map and then overlay city names on it using ggplot.

Creating Geographical Data with sf

To begin, we need to load the necessary libraries: ggplot2 for plotting and sf for geographical data manipulation.

library(ggplot2)
library(sf)

# Create a simple polygon representing our map
df <- st_polygon(list(cbind(c(0, 1, 1, 0, 0), c(0, 0, 1, 1, 0)))) |&gt;
  list(st_point(c(0.25, 0.25)), st_point(c(0.75, 0.75))) |&gt;
  st_sfc(crs = "WGS84") |&gt;
  st_as_sf() |&gt;
  within(lab <- c("", "City 1", "City 2"))

In this example, we create a simple polygon with vertices at (0, 0), (1, 0), (1, 1), and back to (0, 0). We then add two points, one at (0.25, 0.25) and another at (0.75, 0.75), which will serve as the locations for our city names.

Shifting Text Labels with ggplot

Now that we have created our geographical data using sf, let’s focus on shifting text labels outside their borders using ggplot.

The geom_sf_text function in ggplot2 is used to add text labels to a geospatial map. However, by default, these labels will be placed inside the corresponding polygons.

To shift these labels outside their borders, we can utilize the nudge_x and nudge_y parameters within the geom_sf_text function.

ggplot(df) +
  geom_sf(fill = "white") +
  geom_sf_text(aes(label = lab), size = 5, nudge_x = 0.05, nudge_y = 0.05)

In this example, we use nudge_x and nudge_y to shift the text labels by an arbitrary amount of 0.05. This will result in the city names being placed slightly outside their corresponding borders.

Vectorized Inputs for Label Positioning

However, if you prefer to control the exact position of each label, these parameters take vectorized inputs:

ggplot(df) +
  geom_sf(fill = "white") +
  geom_sf_text(aes(label = lab), size = 5, 
               nudge_x = c(0, -0.05, 0.05), 
               nudge_y = c(0, -0.05, 0.05))

In this example, we use vectorized inputs to position the labels at specific locations within their polygons.

Conclusion

Shifting text labels outside their borders can be achieved using ggplot and the sf package in R. By utilizing the nudge_x and nudge_y parameters within the geom_sf_text function, you can control the exact position of each label to suit your specific needs.

Remember to always explore the various options available in ggplot2, as they often provide a range of creative possibilities for visualizing data.

Note: The provided R code examples use an empty dataframe df and do not directly map to the stack overflow post. It’s meant to serve as a starting point for exploring how to achieve similar results with ggplot and sf packages.

Last modified on 2025-01-02