How can I add a line to one of the facets? <pre><code>ggplot(all, aes(x=area, y=nq)) + geom_point(size=0.5) + geom_abline(data = levelnew, aes(intercept=log10(exp(interceptmax)), slope=fslope)) + #shifted regression line scale_y_log10(labels = function(y) format(y, scientific = FALSE)) + scale_x_log10(labels = function(x) format(x, scientific = FALSE)) + facet_wrap(~levels) + theme_bw() + theme(panel.grid.major = element_line(colour = "#808080")) </code></pre> <p>And I get this figure</p> <p><a href="https://i.stack.imgur.com/VIMue.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/VIMue.png" alt="enter image description here"></a></p> <p>Now I want to add <strong>one geom_line</strong> to one of the facets. Basically, I wanted to have a dotted line (Say x=10,000) in only the <strong>major</strong> panel. How can I do this?</p>