A dialect continuum, or dialect area, was defined by Leonard Bloomfield as a range of dialects spoken across some geographical area that differ only slightly between neighboring areas, but as one travels in any direction, these differences accumulate such that speakers from opposite ends of the continuum are no longer mutually intelligible. (It is analogous to a ring species in evolutionary biology.) The lines we can draw between areas that differ with respect to any feature of language are called isoglosses. According to the Ausbausprache - Abstandsprache - Dachsprache paradigm, these dialects can be considered Abstandsprachen (i.e., as stand-alone languages). However, they can be seen as dialects of a single language, provided that a common standard language, through which communication is possible, exists.
There are occasions when various nations of the same linguistic origins occupy the same territory and thus speak the same dialect, but have split standard languages located at different parts of the continuum, sometimes causing doubt as to precisely which language the dialect in question is a member of. Examples include regions such as Kashmir in which local Muslims declare their language Urdu; Sikhs, Punjabi; and Hindus, Hindi. Similar complications arise across much of the former Yugoslavia whereby Bosniaks, Croats and Serbs may speak the same dialect within the same region, yet all have separate standard languages.
In sociolinguistics, a language continuum is said to exist when two or more different languages or dialects merge one into the other(s) without a definable boundary. This happens, for example, across large parts of India. Historically, it also happened in various parts of Europe, for example in a line stretching from Portuguese to Walloon (in Belgium); from Portuguese to the southern Italian dialects; and between German and Dutch. Within the last 100 years or so, however, the increasing dominance of nation-states and their standard languages has been steadily eliminating the non-standard dialects of which these language continua were formed, making the boundaries ever more abrupt and well-defined.
Arabic is a classic case of diglossia. The standard written language, Modern Standard Arabic, is based on the Classical Arabic of the Qur'an, while the modern vernacular dialects (or languages) —which form a dialect continuum reaching from the Maghreb in North Western Africa through Egypt, Sudan, and the Fertile Crescent to the Arabian Peninsula and Iraq—have diverged widely from that. The difference between the written standard and the vernaculars is also apparent in the written language and so children have to be taught Modern Standard Arabic in school in order to be able to understand it.
The spoken variants of Chinese are highly divergent, forming a continuum comparable to that of the Romance languages. However, all the variants more or less share a common written language, though there are vernacular variations in vocabulary, grammar, and orthography.
The written language originally shared by all dialects was Classical Chinese, which was in normal use up until the early 20th century. In pre-modern times, Northern Baihua grew up alongside Classical Chinese as a standard vernacular dialect. The modern standard dialect, Putonghua (often called Mandarin), is largely based on Baihua.
Within the dialects, gradations do exist between pure local vernacular and the more refined speech of the better educated that incorporates elements from the standard language or written language.
The development of the divergent Chinese languages was made much easier because the characters used for writing Chinese are not tied closely to pronunciation as alphabetic or syllabic scripts are. In other words, a Cantonese speaker may write his or her language much the same as a Mandarin speaker and yet pronounce the written text in an entirely different manner (see Diglossia: Chinese for more information).
Mandarin, in its broader sense, encompasses numerous regional dialects spread across the northern half of China as well as the south-western regions. These dialects are mutually intelligible when the proximity is close but at the two extreme ends of the continuum, speakers are not able to communicate with one another. An example would be a speaker of Harbin dialect (a form of Northeastern Mandarin) cannot understand a speaker of Sichuanese Mandarin (but a speaker of Sichuanese Mandarin can understand Harbin dialect due to its high similarity with standard Mandarin).
Yue is a southern Chinese language used in the western half of the Guangdong province and the eastern and southern regions of Guangxi in China. Numerous variations of Yue exist, with the variant used in Guangzhou city (Cantonese) considered the standard form. This standard form is also used in Hong Kong and Macau due to migration of Guangzhou natives to these two regions.
Min Nan is a south-eastern Chinese language used in southern parts of Fujian province, Taiwan, the northeastern part of Guangdong province as well as the Hainan province. Apart from Hainan, this long stretch of coastal region forms a dialect continuum.
The Germanic languages and dialects of Scandinavia are a classic example of a dialect continuum, from Swedish dialects in Finland, to Swedish, Gutnish, Elfdalian, Scanian, Danish, Norwegian (Bokmål and Nynorsk), Faroese, Icelandic, as well as many local dialects of the respective languages. The Continental North Germanic languages (Swedish, Danish, and Norwegian) are close enough and intelligible enough that some consider them to be dialects of the same language, whereas the Insular ones (Icelandic and Faroese) are not immediately intelligible to the other North Germanic speakers.
The many dialects making up German (belonging either to Low German or High German subdivisions) form a dialect continuum. Dutch and Frisian are generally included within this continuum, though the transition between the German dialects mentioned above, and the Dutch and Frisian dialects is far less gradual than between the various German dialects internally.
Modern linguistic studies focusing specifically on the relation between Dutch and German border dialects have shown that rather than forming a gradual near unnoticeable transition, as previously assumed, these dialects rather show the basic signs of a contact language. This is explained by the fact that the historical Old and Middle Dutch language area largely corresponded with the portion of Northwestern Europe that was economically focussed on the Dutch-speaking cities of Bruges and Ghent (later followed by Antwerp and Amsterdam) resulting in a mental socio-economical border greatly limiting interaction. Hence, though intelligibility exists, the relation between the two has been said to be more akin to a mini-Sprachbund than a true continuum.
Many of the Indic languages of Northern India (that includes Assam Valley as for the language Assamese) and Pakistan form a dialect continuum. What is called "Hindi" in India is frequently Standard Hindi, the Sanskritized version of the colloquial Hindustani spoken in the Delhi area since the Mughals. However, the term Hindi is also used for most of the central Indic dialects from Bihar to Rajasthan, and more widely some of the Eastern and Northern dialects too. The Indo-Aryan prakrits also gave rise to languages like Gujarati, Assamese, Maithili, Bengali, Oriya, Nepali, Marathi, and Punjabi, which are not considered to be Hindi despite being part of the same dialect continuum.
The western continuum of Romance languages, which comprises, from West to East: In Portugal, Portuguese; In Spain, Galician, Leonese or Asturian, Castilian or Spanish, Aragonese and Catalan or Valencian; In France, Occitan, Franco-Provençal and standard French; in Italy, Italian and in Switzerland, Romansh as well as other languages with fewer speakers, is sometimes presented as another example, although the major languages in this group have had separate standards for longer than the languages in the continental West Germanic group, and are not commonly classified as dialects of a common language. In recent centuries, the intermediate dialects which existed between the major Romance languages have been moving toward extinction, as their speakers have switched to varieties closer to the more prestigious national standards. This process has been most notable in France, owing to the French government's refusal to recognise minority languages, but has occurred to some extent in all Western Romance speaking countries. Language change has also threatened the survival of stateless languages with existing literary standards, such as Occitan.
A less arguable example of a dialect continuum are the Romance languages of Italy. For many decades since its unification, the above attitude of the French government was reflected in Rome by the Italian government which affected the adjoining dialects of this continuum spoken in Northern Italy. These include Lombard, Venetian and Piedmontese among others. Over the years, however, under pressure from the Northern League, the Italian government has yielded in allowing public signs and other media to use both local and national standard dialects in most affected areas.
The eastern Romance continuum is dominated by Romanian in many respects. Romanian is spoken throughout Romania and its dialects meet the Moldovan registers spoken across the border in Moldova. This too has been a familiar issue whereby Romanians believe the Moldovan language to be an accent (grai) of Romanian and some separatist political forces in Moldova Republic claim that Moldovan is a separate language. Outside Romania across the other south-east European countries, various Romanian language groups are to be found: pockets of various Romanian and Aromanian subgroups continue to live throughout Serbia, Republic of Macedonia, Greece, Albania and Croatia (in Istria).
The Slavic sub-groups of West and East Slavic could also be considered distinct dialect systems. East Slavic consists of: The Russian, Belarusian, Carpatho-Rusyn and Ukrainian languages. The Polish, Slovak and Czech languages, which are in turn closely connected to the Sorbian languages, spoken by the Slavic populations of eastern Germany, form the second. The dialects of both sections are linked by a chain of intelligibility with the west/east classification pertaining more to politically inspired divisions. Together they may be classed as North Slavic, especially when discussed in relation to the South Slavic dialects from whom the speakers are traditionally separated owing to the heavy concentration of the principal non-Slavic populations of Romania, Hungary and Austria.
A separate south Slavic dialect continuum features, among others, the Serbo-Croatian group. This is a network of several major dialects and three national literary standard languages: Bosnian, Croatian and Serbian. These form with the Slovene language the western branch of South Slavic dialects which are in turn linked to an eastern branch, comprising national literary standards Bulgarian and Macedonian which properly form a dialect continuum and share a set of grammatical features that set them apart from all other Slavic languages, with the Bulgarian standard being based on the more eastern dialects, and the Macedonian standard being based on the more western dialects. Unlike the above scenario (east/west Slavic), the barrier between east south Slavic and west south Slavic is natural and not political: the speakers' ancestors inhabited their respective lands having taken alternative routes thus being apart for some generations. Because of this, an intermediate dialect linking western and eastern variations came into existence over time: this is called Torlakian and is spoken on the fringes of Bulgaria, Republic of Macedonia (northern) and Serbia (eastern).
Turkic languages are best described as a dialect continuum. Geographically this continuum starts at the Balkans in the west with Balkan Turkish, includes Turkish in Turkey and Azerbaijani language in Azerbaijan, extends into Iran with Azeri and Khalaj, into Iraq with Turkmen, across Central Asia to include Turkmenistan, Uzbekistan, Kazakhstan, Kyrgyzstan, to southern Regions of Tajikistan and into Afghanistan. In the south, this continuum starts in northern Afghanistan, northward to the Chuvashia. In the east it extends to the Republic of Tuva, the Xinjiang autonomous region in Western China with the Uyghur language and into Mongolia with Khoton. This entire territory is inhabited by Turkic speaking peoples. There are three varieties of Turkic which are geographically outside this continuum: Chuvash, Yakut and Dolgan. These languages have been geographically separated from the other Turkic languages for extensive period of time and Chuvash language stands out as the most divergent from other Turkic languages. There are also Gagauz speakers in the Moldavia and Urum Speakers in Georgia.
The Turkic continuum makes internal genetic classification of the languages problematic. Chuvash and Yakut are generally classified as significantly distinct, while the remaining Turkic languages are quite similar, with a high degree of mutual intelligibility between not only geographically adjacent varieties, but also between varieties which may be some distance apart. Structurally the Turkic languages are very close to one another, and share basic features such as SOV word order, vowel harmony, and agglutination.
The Persian language in its various varieties – Persian (Iran), Dari (Afghanistan) and Tajik (Tajikistan and other parts of the former Soviet Union) – is representative of a dialect continuum. Although official and written forms of the language vary less from one another, spoken Tajiki of Uzbekistan would be virtually incomprehensible to a Persian-speaker of the Persian Gulf islands, and vice versa . The divergence of Tajik was accelerated by the shift from the Perso-Arabic alphabet to a Cyrillic one under the Soviets. Western dialects of Persian show greater influence from Arabic and Oghuz Turkic languages, while Dari and Tajiki tend to preserve many classical features in grammar and vocabulary.
Cree is a group of closely related Algonquian languages in Canada, which is distributed from Alberta to Labrador. These languages form the Cree-Montagnais-Naskapi dialect continuum with around 117,410 speakers. These languages can be roughly classified into nine groups. From west to east, they are:
Various Cree languages are used as languages of instruction and taught as subjects, for example, Plains Cree, Eastern Cree, Montagnais, etc. Mutual intelligibility between some dialects can be low. There is no accepted standard Cree dialect.  
Ojibwa is a group of closely related Algonquian languages in Canada, which is distributed from British Columbia to Quebec, and the United States, distributed from Montana to Michigan, with diaspora communities in Kansas and Oklahoma. Together with the Cree, the Ojibwe dialect continuum forms their own continuum, but with the Oji-Cree language of this continuum joining to the Cree–Montagnais–Naskapi dialect continuum through Swampy Cree. The Ojibwe continuum has 70,606 speakers. Roughly from northwest to southeast, they dialects are:
Unlike the Cree–Montagnais–Naskapi dialect continuum with distinct n/y/l/r/ð(th) dialect characteristics and noticeable west-east k/č(ch) axis, the Ojibwe continuum is marked with vowel syncope along the west-east axis and ∅/n along the north-south axis.