For visual flight rules (VFR), the minimum visibility must be 3 miles. This applies to flying 1,000 feet above the clouds, 500 feet below the clouds, or a visibility line 2,000 feet in the clouds. If these minimums cannot be met, the pilot will have to use Instrument Flight Rules (IFR), as well.
The altitude of Class C is anywhere from ground level to 4,000 feet. Ground is considered airport elevation, or the closest airport or Air Traffic Control (ATC) tower that the airplane is flying to or from. For example, if the airport elevation is 2,000 feet above sea level, the ceiling of Class C airspace would be 2,000 plus 4,000 feet, or 6,000 feet above sea level.
Horizontal space is the space surrounding an airplane's closest ATC. The airspace is mushroom shaped. From the surface to 1,200 feet, the airspace is a radius of 5.75 miles from the ATC tower. This is the stalk of the mushroom, with a diameter of 11.5 miles with the ATC at the center. From 1,200 feet to 4,000 feet, the radius becomes 11.5 miles. This is the head of the mushroom, having a diameter of 23 miles, with the ATC tower at its center.
Prior to entering Class C airspace, the pilot must establish communication with the ATC tower. This is mandatory. If the Class C space overlaps restricted airspace, the restrictions supersede the Class C space rating. For example, a military base may be in a Class C area, but the space is restricted to military planes only. Pilots must comply with all restrictions or prohibitions.