Enclave and exclave

An enclave is a territory (or a part of one) that is entirely surrounded by the territory of one other state. Enclaves may also exist within territorial waters. "Enclave" is sometimes used improperly to denote a territory that is only partly surrounded by another state. The Vatican City State and San Marino, both enclaved by Italy, and Lesotho, enclaved by South Africa, are completely enclaved sovereign states.
An exclave is a portion of a state or territory geographically separated from the main part by surrounding alien territory (of one or more states). Many exclaves are also enclaves, but are not necessarily so; an exclave can be surrounded by several states. The Azerbaijani exclave of Nakhchivan is an example of an exclave that is not an enclave (bordering Armenia, Turkey and Iran).
Semi-enclaves and semi-exclaves are areas that, except for possessing an unsurrounded sea border (a coastline contiguous with international waters), would otherwise be enclaves or exclaves. Enclaves and semi-enclaves can exist as independent states (Monaco, The Gambia and Brunei are semi-enclaves), while exclaves and semi-exclaves always constitute just a part of a sovereign state (like the Kaliningrad Oblast).
A pene-exclave is a part of the territory of one country that can be conveniently approached—in particular, by wheeled traffic—only through the territory of another country. Pene-exclaves are also called functional exclaves or practical exclaves. Many pene-exclaves partially border their own territorial waters (i.e., they are not surrounded by other nations' territorial waters), such as Point Roberts, Washington and Minnesota's Northwest Angle. A pene-exclave can also exist entirely on land, such as when intervening mountains render a territory inaccessible from other parts of a country except through alien territory. A commonly cited example is the Kleinwalsertal, a valley part of Vorarlberg, Austria, that is accessible only from Germany to the north.
Origin and usage.
The word "enclave" is French and first appeared in the mid-15th century as a derivative of the verb "enclaver" (1283), from the colloquial Latin "inclavare" (to close with a key). Originally, it was a term of property law that denoted the situation of a land or parcel of land surrounded by land owned by a different owner, and that could not be reached for its exploitation in a practical and sufficient manner without crossing the surrounding land. In law, this created a "servitude" of passage for the benefit of the owner of the surrounded land. The first diplomatic document to contain the word "enclave" was the Treaty of Madrid, signed in 1526.
Later, the term enclave began to be used also to refer to parcels of countries, counties, fiefs, communes, towns, parishes, etc. that were surrounded by alien territory. This French word eventually entered the English and other languages to denote the same concept, although local terms have continued to be used. In India, the word "pocket" is often used as a synonym for enclave (such as "the pockets of Puducherry district"). In British administrative history, subnational enclaves were usually called detachments or detached parts, and national enclaves as detached districts or detached dominions. In English ecclesiastic history, subnational enclaves were known as peculiars (see also Royal Peculiar).
The word "exclave" is a logically extended back-formation of "enclave".
Characteristics.
Enclaves exist for a variety of historical, political and geographical reasons. For example, in the feudal system in Europe, the ownership of feudal domains was often transferred or partitioned, either through purchase and sale or through inheritance, and often such domains were or came to be surrounded by other domains. In particular, this state of affairs persisted into the 19th century in the Holy Roman Empire, and these domains (principalities, etc.) exhibited many of the characteristics of sovereign states. Prior to 1866 Prussia alone consisted of more than 270 discontiguous pieces of territory.
Residing in an enclave within another country has often involved difficulties in such areas as passage rights, importing goods, currency, provision of utilities and health services, and host nation cooperation. Thus, over time, enclaves have tended to be eliminated. For example, two-thirds of the then-existing national-level enclaves were extinguished on 1 August 2015, when the governments of India and Bangladesh implemented a Land Boundary Agreement that exchanged 162 first-order enclaves (111 Indian and 51 Bangladeshi). This exchange thus effectively de-enclaved another two dozen second-order enclaves and one third-order enclave, eliminating 197 of the Indo-Bangladesh enclaves in all. The residents in these enclaves had complained of being effectively stateless. Only Bangladesh's Dahagram–Angarpota enclave remained.
Netherlands and Belgium though decided to keep the enclave and exclave system in Baarle. As both Netherlands and Belgium are members of the European Union and Schengen Area, people, goods and services flow freely with little or no restrictions.
Enclave versus exclave.
For illustration, in the figure (above), A1 is a semi-enclave (attached to C and also bounded by water that only touches C's territorial water). Although A2 is an exclave of A, it cannot be classed as an enclave because it shares borders with B and C. The territory A3 is both an exclave of A and an enclave from the viewpoint of B. The singular territory D, although an enclave, is not an exclave.
True enclaves.
An enclave is a part of the territory of a state that is enclosed within the territory of another state. To distinguish the parts of a state entirely enclosed in a single other state, they are called true enclaves. A true enclave cannot be reached without passing through the territory of a single other state that surrounds it. "Vinokurov (2007)" calls this the restrictive definition of "enclave" given by international law, which thus "comprises only so-called 'true enclaves'". Two examples are Büsingen am Hochrhein, a true enclave of Germany, and Campione d'Italia, a true enclave of Italy, both of which are surrounded by Switzerland.
The definition of a territory comprises both land territory and territorial waters. In the case of enclaves in territorial waters, they are called maritime (those surrounded by territorial sea) or lacustrine (if in a lake) enclaves. Most of the true national-level enclaves now existing are in Asia and Europe. While subnational enclaves are numerous the world over, there are only a few national-level true enclaves in Africa, Australia and the Americas (each such enclave being surrounded by the territorial waters of another country).
An historical example is West Berlin before the reunification of Germany. Since 1945, all of Berlin was ruled "de jure" by the four Allied powers. However, the East German government and the Soviet Union treated East Berlin as an integral part of East Germany, so West Berlin was a "de facto" enclave within East Germany. Also, 12 small West Berlin enclaves, such as Steinstücken, were separated from the city, some by only a few meters.
Enclaved countries.
Three nations qualify as completely surrounded by another country's land and/or internal waters: 
The Republic of Artsakh, a disputed territory not recognised by any UN member states, controls part of Nagorno-Karabakh, which is an enclave within Azerbaijan.
Historically, four Bantustans (or "Black homelands") of South Africa were granted nominal independence, unrecognized internationally, by the Apartheidist government from 1976 until their reabsorption in 1994. Others remained under government rule from 1948 to 1994. Being heavily partitioned, various parts of these Bantustans were true enclaves.
The United States' constitutional principle of tribal sovereignty treats federally-recognized Indian reservations as quasi-independent enclaves.
True exclaves.
"True exclave" is an extension of the concept of "true enclave". In order to access a true exclave from the mainland, a traveller must go through the territory of at least one other state. Examples include:
Related constructs and terms.
Semi-enclaves and semi-exclaves.
Semi-enclaves and semi-exclaves are areas that, except for possessing an unsurrounded sea border, would otherwise be enclaves or exclaves. Semi-enclaves can exist as independent states that border only one other state, such as Monaco, the Gambia and Brunei. "Vinokurov (2007)" declares, "Technically, Portugal, Denmark, and Canada also border only one foreign state, but they are not enclosed in the geographical, political, or economic sense. They have vast access to international waters. At the same time, there are states that, although in possession of sea access, are still enclosed by the territories of a foreign state." Therefore, a quantitative principle applies: "the land boundary must be longer than the coastline." Thus a state is classified as a "sovereign semi-enclave" if it borders on just one state, and its land boundary is longer than its sea coastline.
Vinokurov affirms that "no similar quantitative criterion is needed to define the scope of non-sovereign semi-enclaves/exclaves." Examples include:
Subnational enclaves and exclaves.
Sometimes, administrative divisions of a country, for historical or practical reasons, caused some areas to belong to one division while being attached to another. Examples include:
"Practical" enclaves, exclaves and inaccessible districts.
The term -exclave was defined in "Robinson (1959)" as "parts of the territory of one country that can be approached conveniently – in particular by wheeled traffic – only through the territory of another country." Thus, a "pene-exclave", although having land borders, is not completely surrounded by the other's land or territorial waters. "Catudal (1974)" and "Vinokurov (2007)" further elaborate upon examples, including Point Roberts. "Although physical connections by water with Point Roberts are entirely within the sovereignty of the United States, land access is only possible through Canada."
Pene-enclaves are also called functional enclaves or practical enclaves. They can exhibit continuity of state territory across territorial waters but, nevertheless, a discontinuity on land, such as in the case of Point Roberts. Along rivers that change course, pene-enclaves can be observed as complexes comprising many small pene-enclaves. A pene-enclave can also exist entirely on land, such as when intervening mountains render a territory, although geographically attached, inaccessible from other parts of a country except through alien territory. A commonly cited example is the Kleinwalsertal, a valley part of Vorarlberg, Austria, that is only accessible from Germany to the north, being separated from the rest of Austria by high mountains traversed by no roads. Another example is the Spanish village of Os de Civís, accessible from Andorra.
Hence, such areas are enclaves or exclaves "for practical purposes", without meeting the strict definition. Many pene-exclaves partially border the sea or another body of water, which comprises their own territorial waters (i.e., they are not surrounded by other nations' territorial waters). They border their own territorial waters in addition to a land border with another country, and hence they are not true exclaves. Still, one cannot travel to them on land without going through another country. Attribution of a pene-enclave status to a territory can sometimes be disputed, depending on whether the territory is considered to be practically inaccessible from the mainland or not.
Enclaves within enclaves.
It is possible for an enclave of one country to be completely surrounded by a part of another country that is itself an enclave of the first country. These enclaves are sometimes called "counter-enclaves". Two such complexes containing them exist currently:
The former complex of enclaves at Cooch Behar district included 24 second-order enclaves and one small third-order enclave called "Dahala Khagrabari #51": a piece of India within a part of Bangladesh, within a part of India, within Bangladesh. The Indo-Bangladesh enclaves were exchanged on 31 July 2015 by the ratified Land Boundary Agreement, and Dahala Khagrabari was ceded to Bangladesh.
Ethnic enclaves.
An ethnic enclave is a community of an ethnic group inside an area in which another ethnic group predominates. Ghettos, Little Italys, barrios and Chinatowns are examples. These areas may have a separate language, culture and economic system.
Extraterritoriality.
Diplomatic missions, such as embassies and consulates, as well as military bases, are usually exempted from the jurisdiction of the host country, i.e., the laws of the host nation in which an embassy is located do not typically apply to the land of the embassy or base itself. This exemption from the jurisdiction of the host country is defined as extraterritoriality. Areas and buildings enjoying some forms of extraterritoriality are not true enclaves since, in all cases, the host country retains full sovereignty. In addition to embassies, some other areas enjoy a limited form of extraterritoriality.
Examples of this include:
Land owned by a foreign country.
One or more parcels/holdings of land in most countries is owned by other countries. Most instances are exempt from taxes. In the special case of embassies/consulates these enjoy special privileges driven by international consensus particularly the mutual wish to ensure free diplomatic missions, such as being exempt from major hindrances and host-country arrests in ordinary times on the premises. Most non-embassy lands in such ownership are also not enclaves as they fall legally short of "extraterritoriality", they are subject to alike court jurisdiction as before their grant/sale in most matters. Nonetheless, for a person's offence against the property itself, equally valid jurisdiction in criminal matters is more likely than elsewhere, assuming the perpetrator is found in the prosecuting authority's homeland. Devoid of permanent residents, formally defined new sovereignty is not warranted or asserted in the examples below. Nonetheless, minor laws, especially on flag flying, are sometimes relaxed to accommodate the needs of the accommodated nation's monument.
Embassies enjoy many different legal statuses approaching quasi-sovereignty, depending on the agreements reached and in practice upheld from time-to-time by host nations. Subject to hosts adhering to basic due process of international law, including giving warnings, the enforced reduction of scope of a foreign embassy has always been a possibility, even to the point of expelling the foreign embassy entirely, usually on a breakdown of relations, in reaction to extreme actions such as espionage, or as another form of sanction. The same seems to be possible in profit-driven moving or drilling under any of the sites below, providing safeguards as the structure or a new replacement site. The same possible curtailments and alterations never apply to proper exclaves.
Examples of such land other than for diplomatic missions are:
Unusual cross-border transport channels.
National railway passing through another state's territory.
Changes in borders can make a railway that was previously located solely within a country traverse the new borders. Since diverting a railway is expensive, this arrangement may last a long time. This may mean that doors on passenger trains are locked and guarded to prevent illicit entry and exit while the train is temporarily in another country. Borders can also be in the "wrong" place, forcing railways into difficult terrain. In large parts of Europe, where the Schengen Area has eliminated border controls when travelling between its 27 member countries, this problem no longer exists, and railways can criss-cross borders with no need for border controls or locked trains.
Examples include:
Highway of one state passing through another state's territory.
This arrangement is less common as highways are more easily re-aligned. Examples include: