雅思聽力:地理課程(4/4)

You'll all have used one at some stage of your life already.Let's consider the benefits of maps from a geographer's perspective. Maps can be folded and put in a pocket and can provide a great store of reference when they're collected into an atlas. They can depict the physical features of the entire planet if necessary, or, just a small part of it in much greater detail. But there is a drawback. You can't exactly replicate something that is three-dimensional, like our planet, on a flat piece of paper, because paper has only two dimensions, and that means there'll always be a certain degree of distortion on a map. It can't be avoided. We can also use aerial photographs, pictures taken by cameras at high altitude above the earth. These are great for showing all kinds of geographical features that are not easy to see from the ground. You can easily illustrate areas of diseased trees or how much traffic is on the roads at a given time or information about deep sea beds, for example.