Axes tick marks at extremes of axes do not align with panel border

Question

I am aware ggplot by default puts 'padding' between the axes and the data. I wish for the origin of the axes to be an actual number, e.g. 0. I know this can be done using scale_y_continuous(expand = c(0, 0)) and scale_x_continuous(expand = c(0, 0)), however without the 'padding' the tick marks do not align correctly with the panel borders. It is as if they are not positioned correctly.

Consider this using mtcars data:

library(ggplot2)
p <- ggplot(mtcars, aes(mpg, wt)) + 
  geom_point() + 
  scale_y_continuous(expand =  c(0, 0), breaks = seq(0, 5, by = 1), limits = c(0, 5)) +
  scale_x_continuous(expand = c(0, 0), breaks = seq(10, 35, by = 5), limits = c(10, 35))

This returns a plot without padding, but you cannot really make out the misalignment yet because the panel border is white.

Now, plot this (panel border has been defined):

p + 
  theme(
    panel.border = element_rect(size= 1, fill=NA),
    axis.ticks = element_line(size = 1, colour ="black"))

The tick at the top of the y axis and the tick at the right of the x axis are not aligned. It is now clear because the panel border is black. I thought perhaps I could mess around with the thickness of the ticks but it does not help. I also thought it was something to do with the major and minor lines of the panel but the following doesn't make a difference:

p + 
  theme(
    panel.border = element_rect(size= 1, fill=NA),
    axis.ticks = element_line(size = 1, colour ="black"),
    panel.grid.major = element_blank(),
    panel.grid.minor = element_blank())

Interestingly, if I remove the panel border and instead add in a defined x and y axis line it does look a bit better because it's harder to see the misalignment unless you really zoom in:

  p +
  theme(
    axis.line.x = element_line(size = 0.5, linetype = "solid", colour = "black"),
    axis.line.y = element_line(size = 0.5, linetype = "solid", colour = "black"),
    axis.ticks = element_line(size = 0.5, colour ="black"),
    panel.border = element_blank())

I am not satisfied with the answer given in Tick marks misaligned with panel in ggplot2 [R] and think there must be a way around this?

Any thoughts? I am missing something here...

teunbrand teunbrand · Accepted Answer · 2021-02-06T13:59:28

The accepted answer to the question you've linked to is correct, this visual misalignment is caused by the panel clipping that occurs. What that answer doesn't tell you is that you can disable the clipping in coord_cartesian(clip = "off"), and instead that answer goes to this roundabout way of adjusting the clipping in the gtable.

Below is an example of turning the clipping off.

library(ggplot2)

ggplot(mtcars, aes(mpg, wt)) + 
  geom_point() + 
  scale_y_continuous(expand =  c(0, 0), breaks = seq(0, 5, by = 1), limits = c(0, 5)) +
  scale_x_continuous(expand = c(0, 0), breaks = seq(10, 35, by = 5), limits = c(10, 35)) +
  coord_cartesian(clip = "off") +
  theme(panel.border = element_rect(size = 1, fill = NA),
        axis.ticks = element_line(size = 1))
#> Warning: Removed 3 rows containing missing values (geom_point).

I'll notify the answer to that other question of the coord_cartesian() option.

Axes tick marks at extremes of axes do not align with panel border

1 Answers