Visualize complex data with subplots by Garrett Grolemund.
From the post:
I think of graphs as a type of visual summary for data. Yet I rarely see graphs used this way within visualizations. Consider tile plots. They group data into 2d bins and then summarize each group with a number. This approach is a go-to tool for understanding overplotted data, but it discards a lot of information. Since we’re already using graphs, why not summarize the data in each bin visually? In the same space that we devote to a single colored tile, we can draw a subplot that retains enough information to display interesting patterns. Take, for example, this visualization of the WikiLeaks Afghanistan War Diary. It replaces each tile with a bar graph that shows the number of casualties by type for the specified region. We still get a sense of where the highest frequencies of casualties occur, but we can also see trends. For example, civilian casualties outnumber combatant casualties in the capital city of Kabul.
Garrett also uses subplots to visualize temperature data (1995-2001) that shows:
Surprisingly, the hottest places in the western hemisphere are not those near the equator.
Not useful for every case but subplots are a graphic technique you should keep in mind.