Height above average terrain

HAAT is used extensively in FM radio and television, as it is more important than effective radiated power (ERP) in determining the range of broadcasts (VHF and UHF in particular, as they are line of sight transmissions).

For international coordination, it is officially measured in meters, even by the Federal Communications Commission in the United States, as Canada and Mexico have extensive border zones where stations can be received on either side of the international boundaries.

The FCC has divided the Contiguous United States into three zones for the determination of spacing between FM and TV stations using the same frequencies.

In all zones, maximum ERP for analog TV transmitters is as follows: Zone I (the most densely populated zone) consists of the entire land masses of the following states: Connecticut, Delaware, Illinois, Indiana, Maryland, Massachusetts, New Jersey, Ohio, Pennsylvania, Rhode Island, and West Virginia; in addition to the northern and eastern portions of Virginia; the areas of Michigan and southeastern Wisconsin south of 43° 30' north latitude; the coastal strip of Maine; the areas of New Hampshire and Vermont south of 45° north latitude; and the areas of western New York south of 43° 30' north latitude and eastern New York south of 45° north latitude.

One of the most powerful of these stations is WBCT in Grand Rapids, Michigan, which operates at 320,000 watts and 238 meters (781 ft) HAAT.