USGS Map Symbology - CONTROL DATA AND MONUMENTS Aerial photographic roll and frame number* Horizontal control Third order or better, permanent mark With third order or better elevation Check spot elevation Coincident with section corner Unmonumented* Vertical control Third order or better, with tablet Third order or better, recoverable mark Bench mark found at section corner Spot elevation Boundary monument With tablet Without tablet With number and elevation U.S. mineral or location monument