Graphic marks are considered to be symbols when they are agreed to have a certain meaning. This could be a picnic table to identify a park site, or a blue cross to identify a hospital. Others are more specific to maps—the use of a circle to represent a city, for example. The mapmaker assigns a symbol that represents the information he or she wants to bring across to the map user. Good, intuitive symbols can often be presented without defining them in a legend, but for most purposes, we add a legend to ensure clarity.