Fire frequency is derived from fire history. Polygons thus represent areas where fire has burned on the landscape. Each polygon is associated with a count of how many fires have burned there and a date for the last known fire. Areas on the landscape without a polygon do not have known recorded fire history since 1920. Fire is known to have burned frequently on the landscape before Euroamerican settlement and national park designation, but this layer does not reflect frequency from fires prior to 1920.