When I was in college, I had a roommate who was an architecture major. Several years later, I visited him when he was doing graduate study at University of Oklahoma, in Norman. While I was there, I attended a class he was in, in which the students were reporting the results of a project.
The project was about landmarks. Each class member had to give driving directions from a point on campus to a point in town, but the use of street names was forbidden. The directions had to use landmarks only. On the day I attended, the class compared their directions, and mapped the landmarks they used.
It was interesting to see the number and variety of landmarks used, and to note that no two sets of directions were even close to being the same, though many of them took you along the same route. Some landmarks were so obvious that nearly everyone used them. At other times, one might tell you to turn left at the gas station, another would say to turn left at the burger place, and a third had you look for the big purple house and take a left at the next traffic light.
Since then, I've paid attention to what people use, and I've come across some amusing situations in the use of landmarks for directions. For one thing, there's the fact that landmarks sometimes change, as stores change hands and road construction alters things. Near my office, the “Hawthorne Circle” was used as a landmark by many, long after it ceased to be a circle. And the half-joking directions to one friend's house included “take the exit just before where the toll plaza used to be.”
When I lived in the Maryland suburbs of DC, I was looking, one time, for a catalogue store — quite a large place that was, despite its size, not on the main road. I wasn't sure just where it was, so I stopped at a gas station to ask. “Sure,” said the guy, “I can tell you where to find it. Turn left at this light, then right at the second light. Look on the left and you'll see PJ's, and the catalogue store's right next to it.”
His directions were perfect, and I found the place. Only... the store I was looking for was huge. PJ's was a little deli, smaller than one of his garage bays. Who would use that as a landmark? Well, maybe he was being silly. Or maybe he gets his lunch at PJ's, and never has occasion to go into the catalogue store, so which one figures more prominently in his mind?
Then there was a guy I had dinner with during a trip to Boulder, Colorado. A group of us were at a Moroccan restaurant there, and we were talking about other places to eat, and such things around town. And this one guy in the group considered everything relative to the various liquor stores in the area. “Oh, is that the one that's a couple of shops past the liquor store?” “There's a great Chinese place on Arapahoe over by the liquor store.” He was quite consistent with it, and one of the women who was with us wondered what that said about him.
And how many landmarks do you use? I was visiting friends in Rochester, Minnesota, once, and the woman of the couple gave me directions to get to their house from the airport. At one point she had me turn, and then said that I'd see a gas station, then a supermarket, then another gas station, then a bank, or whatever these all were, then I'd pass a field of trees, and then I'd turn on 14th St. When I got there, I started looking for one after another of the landmarks. I found one or two instantly, and then came to route 2, which I drove past, looking for the other landmarks and 14th St.
I soon realized that I'd missed the turn, and backtracked. It turns out that route 2 is 14th St (but guess which way it's marked more clearly), that it really did come up that quickly, and that she had given me five landmarks, including “a field of trees”, in one, single, short block (it's a very small field of trees). That's a bit high on the landmark density scale. When I got to their house I showed the directions to her husband, who just shook his head and offered me a homebrew beer.
 Yes, that's right: I'm a man, and I stopped and asked for directions. Imagine.