Some models, such as maps and charts, are two-dimensional representations of something. We call these graphical models.
Many maps include symbols that represent different things, such as roads, bridges, streams, and campgrounds. A key explains the meaning of each symbol that appears on the map.
If you are traveling in the car and looking for a rest area along the highway, you would look for a specific symbol that represents a rest area on your map.
You might want to know how far it is from your home to the library. On your map, it looks like it is just a few centimeters from one to the other. But what does this mean? You need to find the scale of your map.
Somewhere, off to the side, you will see a line that looks like a ruler. It will be in either customary or metric units. Using the scale on the map, it might tell you that 2 centimeters equals 1 kilometer. You can use this information to calculate how far it is from one place to another.