Considered the founder of the modern Japanese geography for his use of lines of latitude and longitude. A Confucian scholar with Samurai status, Nagakubo was an extensive traveler on official business, his journeys made on behalf of his home domain of Mito. He was author of a Nagasaki kõeki nikki — Diary of an Official Journey to Nagasaki (1767), during which he was given the task of interrogating and supervising the return of a group of castaways from the Mito domain whose ship had been blown off course in 1765 and who had been stranded ever since.
Nagakubo studied with Japan’s most famous astronomers, and published Tensho kanki sho – Brief Explanation of Astronomical Phenomena (1774). As was traditional at the time, his work was influenced by Chinese astronomy but also more recent European discoveries, introduced by the Dutch.
Nagakubo’s first map of China, Daishin Koyozu – Enlarged Map of China under the Ch’ing Dynasty (1785), was based on the map of China in the T’ien Ching Huo Wen (1730), but revised according to maps in the Kuang Yu T’u, the Ta Ch’ing I T’ung Chih (1744), and from the Rekidai Jiseki Zu (1750). As a result, the topographical features of China are more accurate than in its predecessors.
This was followed in 1790, by an atlas of China, Todo Rekidai Shugun Enkaku Chizu – Historical Atlas of Chinese Provinces and Districts under Each Successive Dynasty.
At about the same time, Nagakubo issued the map for which he is now best known, the Chikyū bankoku sankai yochi zen zusetsu – 地球萬國山海輿地全圖說 – Comprehensive Map and Description of the Geography of the Myriad Countries of the Globe. One of the earliest world maps made in Japan, it is a reduced version of Matteo Ricci’s revolutionary world map, Kunyu wanguo quantu – 坤輿萬國全圖 — Complete geographical map of all countries, published in Beijing in 1602. Geographically, Sekisui’s map is a faithful copy of Ricci’s map: it strictly resembles the proportion and shape of the continents, oceans, seas, and islands. However, he made significant improvement on the illustration of Japan and Kuril Islands.