Legend
The legend is a standard element on most layouts. It provides the color and symbol
key look‑up details for the map element. It is comprised of an item (icon, point, line,
polygon) and its label (description of the item). If the layout is being created for a narrow audience such as your work group and the map includes commonly understood
feature types with standard symbology such as county boundaries, water bodies,
elevation, and so on, then these may be granted an exception from inclusion in a
legend. Wider audience maps may also exclude certain given feature types drawn
with standard symbology such as blue water bodies or green land expanses; however,
these are left to the discretion of the map author. Only exclude map layers from a
legend — or the legend itself from the layout — purposefully. Don’t just forget some.
Err on the side of the more legend items the better, since a map is not worth much if
its features cannot be understood. What is obvious to the map author can easily be
unknown to the map viewer.