Legendary fund manager Peter Lynch once said that you shouldn't invest in any idea you couldn't illustrate with a crayon.

Though I'm not much for crayons, I do love the pithiness of that line. We regularly preach the same idea at the Fool: Don't buy what you don't understand. And if you can't simply sketch out a company's business model -- how it actually makes money -- then maybe you shouldn't be investing in it.

I'm willing to guess that most of us have a mummified McDonald's (NYSE: MCD) french fry or two nestled in the darkness under our car's front seat. I know I do, and there's probably a ketchup packet down there too. And we're not the only ones. Whether you're driving on Route 66 or the Champs-Elysees, a McDonald's probably is not too far away. Let's take a look at just how much money McDonald's made last year worldwide. (Note: I'm focusing on revenues here, not earnings.)

Source: McDonald's 2011 10-K.

Think I missed something in this illustration? General thoughts on this exercise? Let me know in the comments section below. And if you haven't already, be sure to follow our McDonald's news and commentary using the Fool's free My Watchlist tool.