A number of Korean dialects are spoken on the Korean Peninsula. The peninsula is extremely mountainous and each dialect's "territory" corresponds closely to the natural boundaries between different geographical regions of Korea. Most of the dialects are named for one of the traditional Eight Provinces of Korea. One is sufficiently distinct from the others to be considered a separate language, the Jeju language.
Dialect zones identified by Shinpei Ogura (1944)
Distribution of tone and length in Korean dialects: tone length no length or tone
Korea is a mountainous country, and this could be the main reason why Korean is divided into numerous small local dialects. There are few clear demarcations, so dialect classification is necessarily to some extent arbitrary.
A common classification, originally introduced by Shinpei Ogura in 1944 and adjusted by later authors, identifies six dialect areas:
Central dialect, Hwanghae, Gyeonggi, Gangwon(Yeongseo) and Chungcheong are usually grouped together. However, many view that only Hwanghae, Gyeonggi, and Gangwon(Yeongseo) dialects are included in the central dialect, while Chungcheong dialect is considered as separate dialect.
Spoken in the historical Yukchin region which is located in the northern part of North Hamgyong Province, far removed from P'yŏng'an, but has more in common with P'yŏng'an dialects than with the surrounding Hamgyŏng dialects. Since it has been isolated from the major changes of Korean language, it has preserved distinct features of Middle Korean. It is the only known tonal Korean language.
A recent statistical analysis of these dialects suggests that the hierarchical structure within these dialects are highly uncertain, meaning that there is no quantitative evidence to support a family-tree-like relationship among them.
Some researchers classify the Korean dialects in Western and Eastern dialects. Compared with Middle Korean, the Western dialects have preserved long vowels, while the Eastern dialects have preserved tones or pitch accent. The Jeju language and some dialects in North Korean make no distinction between vowel length or tone. But the Southeastern dialect and the Northeastern dialect may not be closely related to each other genealogically.
The standard language
In South Korea, Standard Korean (표준어/標準語/pyojun-eo) is defined by the National Institute of the Korean Language as "the modern speech of Seoul widely used by the well-cultivated" (교양있는 사람들이 두루 쓰는 현대 서울말). In practice, it tends not to include features that are found exclusively in Seoul.
Koryo-mar (Autonym: Корё мар/고려말, Standard Korean: 중앙아시아 한국어), usually identified as a descendant of the Hamgyŏng dialect, is spoken by the Koryo-saram, ethnic Koreans in the post-Soviet states of Russia and Central Asia. It consists of a Korean base vocabulary, but takes many loanwords and calques from Russian language. It is mostly based on Hamgyong and Ryukchin dialect, since Koryo-saram people are mainly from the northern part of Hamgyong region.
Sakhalin Korean Language (사할린 한국어), usually identified as a descendant of the southern dialect, is spoken by the Sakhalin Korean.