Removing white spaces around plots in R Markdown / Quarto

R
R tips
Author

Philippe Massicotte

Published

August 15, 2022

When plotting spatial data, such as a geographical map, maintaining a proper aspect ratio is important. Whereas knitr::plot_crop() works fine to crop a file, how can we do the same operation for a figure inside an R Markdown or a Quarto document? Thanks to knitr, this can be done with a hook.

Let’s crop something! Photo by Ant Rozetsky on Unsplash

I will use the polygon of Greenland to illustrate the issue.

greenland <-
  ne_countries(
    country = "greenland",
    returnclass = "sf",
    scale = "medium"
  )

# Find a proper projection
proj <- as.numeric(crsuggest::suggest_crs(greenland)$crs_code[1])
proj
#> [1] 5922

If we plot the map, we can see that there are white spaces around the image to keep the proper aspect ratio. This is not a problem per se, but one might be interested to fill up the ploting area with the actual plot.

```{r plot-original}
greenland |>
  ggplot() +
  geom_sf(size = 0.25) +
  coord_sf(crs = proj) +
  theme(
    plot.background = element_rect(fill = "#3c3c3c"),
    panel.border = element_rect(color = "red", fill = NA),
    panel.grid = element_blank(),
    panel.background = element_rect(fill = "#3c3c3c", color = "red"),
    axis.text = element_blank(),
    axis.ticks = element_blank()
  )
```

Now, I will create a hook named crop that is associated with the knitr::hook_pdfcrop() function.

```{r}
knitr::knit_hooks$set(crop = knitr::hook_pdfcrop)
```
Note

Note that the magick package and probably the underlying system library need to be installed on your system to crop images.

With that, we can use crop: true in a code chunk to call it and crop the displayed graph.

```{r plot-cropped}
#| crop: true
greenland |> 
  ggplot() +
  geom_sf(size = 0.25) + 
  coord_sf(crs = proj) +
  theme(
    plot.background = element_rect(fill = "#3c3c3c"),
    panel.border = element_rect(color = "red", fill = NA),
    panel.grid = element_blank(),
    panel.background = element_rect(fill = "#3c3c3c", color = "red"),
    axis.text = element_blank(),
    axis.ticks = element_blank()
  )
```

VoilΓ  πŸ‘, no more borders around the image.

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