I once overheard a couple in a park that were looking at a sign-posted map of their location. He had just pointed out to her the "You are here" red dot on the map. Her response was puzzled: "How do they know where we are?"

Now, many of you may find this humorous, most likely because you have the reasonable expectation that anybody reading a marked map with a "You are here" indication on it must be where the sign is placed to read it, and that the sign is correct and placed in the relevant location.

But not so fast. Is this just another "common sense" cultural assumption that we have made? If the "You are here" signs at Expo 2010 Shanghai are any indication, there seems to be little attention paid to placing a locator map in the correct location or, more precisely, orienting it in the right direction.

Let me explain.

Here, as every other place in the world, the Chinese follow the universal convention that north is at the top of the map, south at the bottom, east is to the right and west to the left.

So far so good.

Now to properly "orient" yourself on land you need to have the north of the map facing the north of the land. From there, if you want to go east you will know that you need to go right, if west to the left and so on. This is easy enough to do when you have a handheld map. Just turn (orient) the map and yourself so the map is aligned with your position on the ground.

In order to show where you are and which direction you need to go to get someplace, a posted map, that is, one permanently fixed in position, needs to be oriented in the same direction as the topography it represents (that is, north facing north). And here is where the trouble arises.

All the posted maps at the Expo are obsessively fixed with north at the top regardless of which direction they face. This works, of course, when the viewer of the map is truly facing north. But when they and the map they are looking at is not facing north (which, by the way, is the majority of the time), the map ceases to be effective. Worse still, it will send you in the wrong direction.

So here you are at one of the world's greatest events that is expecting 70 million visitors over the next six months and the maps are wonky.

Most visitors will soon learn that they need to disregard the posted maps with their "You are here" indicators and doubt - as the girl of the young couple did - that they really know where you are.

But it is not all bad news. There are thousands of helpful smiling volunteers ready to show you the way and many of the Expo's structures are impressive, massive landmarks and easy to find by sight. But I do wonder how visitors to some remote national park would fare with this method of posted maps and directions.

The author is a human ecologist and environmental consultant dedicated to life-long learning about the Earth's life-support systems, and the intimate connection between the health of the planet and its people.