You want to plot subsets of your data in separate panels.

Use facet_grid() or facet_wrap(), and specify the variables on which to split.

With facet_grid(), you can specify a variable to split the data into vertical subpanels, and another variable to split it into horizontal subpanels (Figure 11-1):

# The base plot
p <- ggplot(mpg, aes(x=displ, y=hwy)) + geom_point()

# Faceted by drv, in vertically arranged subpanels
p + facet_grid(drv ~ .)

# Faceted by cyl, in horizontally arranged subpanels
p + facet_grid(. ~ cyl)

# Split by drv (vertical) and cyl (horizontal)
p + facet_grid(drv ~ cyl)

Figure 11-1. Top: faceting horizontally by drv; bottom left: faceting vertically by cyl; bottom right: faceting in both directions, with both variables