Where do car designers get their inspiration? It's a mystery even to the designers themselves. As they once stood looking at the final prototype for the new 7 Series, Chris Bangle turned to Adrian van Hooydonk, the 7's designer, and asked, "Where did this come from?" van Hooydonk shrugged; he really couldn't say.

In broad terms, BMW's designers get their ideas from the world around them - though not from the world of cars. "If I were to list my influences in car design, I'm afraid you'd have to think pretty synthetically to make sense of them," says Bangle. "Architecture, airplanes, boats, botany, cathedrals, domes … just go through the alphabet."

Bangle fills notebooks with cartoon-like sketches of his travels and observations, with quick captions written in German and English. There's a star chart for locating the Southern Cross; there are notes from last year's World Economic Forum, including a whimsical sketch of Hillary Clinton's begrimed high heels and a free-flowing illustration of the gateway to the Alamo in San Antonio, Texas. Tellingly, there's not a single sketch of a car. Bangle won't comment on his jottings (too personal), but as he closes the journal, he offers a cryptic bit of advice: "Take notes on the world. There will be a test."