What is a common characteristic of all types of maps?

A common characteristic of all types of maps is that they include a legend or key. This element is crucial as it provides the user with the necessary information to understand the symbols and notations used throughout the map. The legend translates complex information about geographical features such as roads, rivers, and political boundaries into comprehensible visual symbols, allowing users to interpret the map accurately.

While other options might be true for various types of maps, they are not universally applicable. For instance, not all maps are drawn to scale; some are more illustrative and do not maintain a proportional representation of distances. Similarly, the color schemes used in maps can vary greatly depending on the purpose and type of the map, so there is no standard set of colors that all maps use. Finally, while many maps aim to represent the Earth's three-dimensional surface, they often do so in a two-dimensional format, thus not all maps effectively convey this characteristic. Hence, the inclusion of a legend or key stands as the strongest commonality among all map types.