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The Tokaras are separated from Amami Ôshima by a section of the [[Kuroshio]] current known as the Shichitô-nada, which historically made migration and trade between the two somewhat more difficult, separating the [[Ryukyuan languages]] from Kyushu dialects of Japanese and creating a natural barrier as well, leading to differences in flora and fauna between the two island groups. The southernmost end of the Kuroshio also forms a similar barrier between Yonaguni and Taiwan, contributing to both natural and human separations between the southern Ryukyus and Taiwan as well.<ref>Smits, ''Maritime Ryukyu'', 17.</ref>

The Tokaras are separated from Amami Ôshima by a section of the [[Kuroshio]] current known as the Shichitô-nada, which historically made migration and trade between the two somewhat more difficult, separating the [[Ryukyuan languages]] from Kyushu dialects of Japanese and creating a natural barrier as well, leading to differences in flora and fauna between the two island groups. The southernmost end of the Kuroshio also forms a similar barrier between Yonaguni and Taiwan, contributing to both natural and human separations between the southern Ryukyus and Taiwan as well.<ref>Smits, ''Maritime Ryukyu'', 17.</ref>

The islands of the Ryûkyû archipelago include both "high" islands formed by volcanic activity (like most of the islands of the Japanese archipelago) and "low" islands made of coral limestone. "High" islands such as Yakushima, Amami Ôshima, Kakeroma, Tokunoshima, Iheya, Kumejima, Tonaki, the Kerama Islands, Iriomote, Yonaguni, and the northern portions of Okinawa and Ishigaki Islands, generally have somewhat acidic soil, and more streams and rivers, while "low" islands such as Tanegashima, Kikaijima, Okinoerabu, Yoron, Miyakojima and the islands immediately surrounding it, Irabu, Tarama, Taketomi, Hateruma, and the central and southern portions of Okinawa and Ishigaki Islands, have more neutral or alkaline soil, fewer streams or rivers, and fewer trees. Springs and underground caves are the primary source of fresh water, and while limestone for building walls, tombs, and other structures is plentiful, lumber for construction or firewood is not.<ref>Gregory Smits, ''Early Ryukyuan History: A New Model'', Univ. of Hawaii Press (2024), 65.</ref> There are no serious mountains in the Ryukyus, and the average height above sea level across the entire archipelago is a tiny fraction of that of the far more mountainous islands of Japan and Taiwan.

The islands of the Ryûkyû archipelago include both "high" islands formed by volcanic activity (like most of the islands of the Japanese archipelago) and "low" islands made of coral limestone. "High" islands such as Yakushima, Amami Ôshima, Kakeroma, Tokunoshima, Iheya, Kumejima, Tonaki, the Kerama Islands, Iriomote, Yonaguni, and the northern portions of Okinawa and Ishigaki Islands, generally have somewhat acidic soil, and more streams and rivers, while "low" islands such as Tanegashima, Kikaijima, Okinoerabu, Yoron, Miyakojima and the islands immediately surrounding it, Irabu, Tarama, Taketomi, Hateruma, and the central and southern portions of Okinawa and Ishigaki Islands, have more neutral or alkaline soil, fewer streams or rivers, and fewer trees. Springs and underground caves are the primary source of fresh water, and while limestone for building walls, tombs, and other structures is plentiful, lumber for construction or firewood is not.<ref>Gregory Smits, ''Early Ryukyuan History: A New Model'', Univ. of Hawaii Press (2024), 64-65.</ref> There are no serious mountains in the Ryukyus, and the average height above sea level across the entire archipelago is a tiny fraction of that of the far more mountainous islands of Japan and Taiwan.

Traditionally, regions of the Ryukyus were referred to by poetic placenames using the word for "mountain" (''san'' or ''zan''). Prior to the unification of the island, Okinawa itself was divided into Hokuzan, Chûzan, and Nanzan. The distant Miyako and Ishigaki Islands were referred to as Taiheizan 太平山, Iheya and Izena, just west of Okinawa, were referred to as Yôhekizan 葉壁山, and the Kerama Islands were called Bashizan 馬歯山.<ref>Kitahara Shûichi. ''A Journey to the Ryukyu Gusuku'' 琉球城紀行, Naha: Miura Creative (2003), 84.</ref>

Traditionally, regions of the Ryukyus were referred to by poetic placenames using the word for "mountain" (''san'' or ''zan''). Prior to the unification of the island, Okinawa itself was divided into Hokuzan, Chûzan, and Nanzan. The distant Miyako and Ishigaki Islands were referred to as Taiheizan 太平山, Iheya and Izena, just west of Okinawa, were referred to as Yôhekizan 葉壁山, and the Kerama Islands were called Bashizan 馬歯山.<ref>Kitahara Shûichi. ''A Journey to the Ryukyu Gusuku'' 琉球城紀行, Naha: Miura Creative (2003), 84.</ref>