Extrality

The major portion of a starport is surrounded by a barrier demarking the limit of Imperial extraterritoriality (often shortened to extrality). The region inside this is under direct Imperial authority and local planetary laws do not apply. Goods may be purchased here without duty, and taxes are limited to a small Imperial income tax and such customs duties as the Imperium levies. Violators of local laws, especially political "criminals," may find asylum and sanctuary from restrictive local regimes, but if the fugitive is sought for an offense that is also a violation of Imperial law (murder, most felonies, and so on), Imperial officials will hold and extradite the fugitive.

Depending on the nature of the planetary government, the extrality limit may be marked by a simple wire fence or more complex barriers resembling the Berlin Wall of old Terra. This usually done to prevent citizens of the planet from leaving without authorization and to enforce local customs laws.

Although, strictly speaking, the law level of the starport permits any weapon to be carried openly, the Imperial laws against property damage, murder and extortion are rigidly enforced by Imperial authorities, backed up by Imperial military forces as necessary. The owners of most businesses frown on open displays of weaponry and will usually refuse to serve walking arsenals. . . and are usually fairly well equipped themselves.

Each facility has its own unique features, and the number of variants is almost equal to the number of downports (that portion of the starport located on the surface of the planet orbital facilities, or highports, are all extraterritorial). Almost every downport has an associated urbanization surrounding the downport (in many cases completely). Residential areas are often allowed inside the extrality barrier for employees of the port and its associated businesses.

Source: GURPS Traveller