You want to set the ratio at which the x- and y-axes are scaled.

Use coord_fixed(). This will result in a 1:1 scaling between the x- and y-axes, as shown in Figure 8-10:

library(gcookbook) # For the data set

sp <- ggplot(marathon, aes(x=Half,y=Full)) + geom_point()

sp + coord_fixed()

Figure 8-10. Left: scatter plot with equal scaling of axes; right: with tick marks at specified positions

The marathon data set contains runners’ marathon and half-marathon times. In this case it might be useful to force the x- and y-axes to have the same scaling.

It’s also helpful to set the tick spacing to be the same, by setting breaks in scale_y_continuous() and scale_x_continuous() (also in Figure 8-10):