A geologic map is a graphical information display that uses a combination of colors, lines, and symbols to depict the composition and structure of geologic materials and their distribution across and beneath the landscape. The graphical display contains both descriptive information about geologic units and structures and an interpretive model of how they were formed. This combination of descriptive and interpretive geologic map information provides a conceptual framework that relates all the geologic elements of an area together so that the position, characteristics, and origin of each element are understood in relation to all other elements. Such a unique synthesis of descriptive and interpretive information makes the geologic map a powerful research tool for understanding the Earth's composition and structure, internal and external processes, and history.