The Technical Bits (for UK)
The Operational Area, which is under positive control of the Company, encompasses the Landing Site, the taxiways, HAAs and IAAs (see below for definitions) and takeoff, climb and approach slopes. It has side surfaces rising upwards and outwards to 100 feet at a gradient of
1:1 from its edges, unpenetrated by obstacles and will be fenced, roped off or otherwise protected from intrusion by unauthorised persons— therefore it should not include a public right-of way. Rope and stakes for demarcation and public control are not obstacles for this purpose.
Final Approach and Takeoff Area (FATO)
This is inside the Safety Area (see below), where the final phase of the approach to hover or landing is completed, and from which takeoff is commenced. It may be square or circular and the minimum size is 1 . x the rotor diameter (popular helicopters are listed later).
Safety Area (SA)
Surrounds the FATO, for reducing damage to helicopters accidentally diverging from it. It is also square or circular, according to the FATO, and the minimum size is 3m or . of the rotor diameter, whichever is the greater. It must be free from obstacles.

The combined size of the FATO and SA should be at least twice the overall length, including rotors, of the helicopter and, where it contains the TLOF (see below), the surface should be firm and not blow away with downwash.
Touchdown and Liftoff Area (TLOF)
A load bearing area for touch down and lift off; it should be free from slopes, to ease passenger embarkation and disembarkation, and not have them walking uphill into tail rotors. The TLOF has a diameter of at least twice the length of the helicopter, including rotors, and is normally contained within the FATO (it's the same minimum size), but may be separate.
Taxiways
Used where the TLOF is remote from the FATO, with a minimum clearance of 1 rotor diameter from obstructions either side of the rotor disc (that is, a minimum overall width of 3 rotor diameters, or 33.9m for the Bell 47).
Helicopter Acceleration Area (HAA)