A legend or key is an explanatory list that defines symbols appearing in a map or chart. These keys usually show a small picture of each of the symbols used on the map, along with a written description of the meaning of each of these symbols. Some symbols, such as a mountain range and waterfall symbols, may resemble the features they represent whereas others, such as restaurants or gas stations, may not be as identifiable. Clarity is important for the reader to be able to focus on the data.