Inou Tadataka was a Japanese surveyor and cartographer. He is known for completing the first map of Japan created using modern surveying techniques.
Inou was born in Kujukuri, a coastal village in Kazusa Province, in what is now Chiba Prefecture, and was adopted by the prosperous Inou family of Sawara, a town in Shimo-Osa Province. He ran the family business, expanding its sake brewing and rice-trading concerns, until he retired at the age of 49. At this time he moved to Edo and became a pupil of astronomer Takahashi Yoshitoki, from whom he learned Western astronomy, geography, and mathematics.
In 1800, after nearly five years of study, the Shogunate permitted Inou to perform a survey of the country using his own money. This task, which consumed the remaining seventeen years of his life, covered the entire coastline and some of the interior of each of the Japanese home islands. During this period Inou reportedly spent 3,736 days making measurements (and travelled 34,913 kilometres), stopping regularly to present the Shogun with maps reflecting his survey's progress. He produced a number of detailed maps of select parts of Japan, mostly in Kyuushuu and Hokkaido.
Inou's magnum opus, his 1:216,000 map of the entire coastline of Japan, remained unfinished at his death in 1818, but was completed by his surveying team in 1821. An atlas collecting all of his survey work, entitled Dai Nihon Enkai Yochi Zenzu (大日本沿海輿地全図 = maps of Japan's coastal area), was published that year. It showed the entire country on eight pages at 1:216,000, 214 pages of select coastal areas at 1:36,000, and three pages of fine detail at 1:432,000. The Inou-zu, many of which are accurate to 1/1000 th of a degree, remained the definitive maps of Japan for nearly a century, and maps based on his work were in use as late as 1924.
In addition to his maps, Inou produced several scholarly works on surveying and mathematics, including Chikyu sokuenjutsu mondo and Kyukatsu en hassenho.