The key is used on a map because it helps to understand a mapLearn about maps and map keys/legends. Understand why map keys are essential to understanding maps, and see some examples of the importance of map keys.
What Is a Map
Just like your house key opens your front door, a map key or legend opens up a map. The map key is what gives you all the information you need for a map to make sense. But first, what exactly is a map? It is a way that we can show different parts of Earth in two dimensions. Maps can show large areas, like the entire planet, or very small areas, like your neighborhood. The purpose of a map is to show how things relate to each other spatially, but more often than not, a map also shows other kinds of information.
For example, a map's purpose might be to show the pattern of the subway system in New York City, the number of people per country in Africa, the location of forests in Canada or the location of monuments in Washington, D.C. These are just a few examples of the types of things that maps portray, but there are literally thousands of other things that maps can show. Being able to see relationships on a map is often much easier to understand than just a verbal or written explanation. This makes maps invaluable tools. But, unless a map has a map key to open it up, it doesn't make very much sense.
Map Key or Legend
A map key or legend is included with a map to unlock it. It gives you the information needed for the map to make sense. Maps often use symbols or colors to represent things, and the map key explains what they mean. Map keys are often boxes in the corner of the map, and the information they give you is essential to understanding the map. Symbols in the key might be pictures or icons that represent different things on the map. Sometimes the map might by colored or shaded, and the key explains what the colors and shades mean. The picture here shows an example of a map key for a typical road map.