Inoh Maps were the first scientific maps of Japan to be prepared based on survey results of Inoh Tadataka (1745-1818)'s team. Each map is revolutionary in the history of Japanese Cartography. Inoh Maps have been used in nautical charting in two ways: in the preparation of British Admiralty charts and in the preparation of Japanese charts at the early stage of what was the then the Hydrographic Department of Japan. Hoyanagi (1974) summarized the scientific achievements of Inoh Tadataka, including his contributions to nautical charting, and these have been quoted in many papers. The Tokyo Geographical Society conducted the 2017 United Kingdom Geo-Tour as one of programs marking the 200th anniversary of his death. Based on research carried out in the United Kingdom in 2016 and 2017, old and new findings are summarized and unresolved issues are presented. The main findings are as follows:
(1) Inoh Small scale Maps held in the United Kingdom have been permanently transferred to The National Archives.
(2) The Royal Navy evaluated Inoh Maps and used them in preparing eight British Admiralty charts of the area around Japan.
(3) Graticule lines of British Admiralty charts are based on the prime meridian of Greenwich; therefore, the location of Japan was established on the world maps.
(4) British Admiralty charts were compiled from Inoh maps with corrections for longitude and transferred from a graticule similar to Sanson–Flamsteed's projection to the graticule of the Mercator projection.
(5) Hydrographic Department of Japan was founded in 1871. Te first Chief Hydrographer Admiral Yanagi Narayoshi ordered the reproduction of approximately 300 Inoh Large scale Maps held by what was then the Ministry of Interior and utilized them for hydrographic survey, the preparation of nautical charts, and sailing directions.
(6) Exact reproduction history of Inoh Small scale Maps held in the United Kingdom from original Inoh Small scale Maps is not known.