Above is map of western Japan, showing almost all the places Katayama was known to have been to: Osaka, the Atago Shrine near Kyoto, Shikoku (the island in the center of the map), Aki (today's western Hiroshima), and Suo (in Yamaguchi), which includes Iwakuni. Hōki Province is now a part of Tottori Prefecture. Katayama's teacher and uncle Shōan might have been located in Sunshu, in today's Shizuoka, roughly 300 miles east of the eastern edge of the map, thus constituting an exception. The more active Hōki-ryū locations in Japan today are all on this map: Hiroshima, Hyogo, Kumamoto, Kyoto, and Osaka. It is only natural for Nakamura sensei to come from this ancient region as well. He began studying Hōki-ryū in Hiroshima, and now resides in Hyogo. (For reference, Tokyo is approximately 450 miles east of this map.)
The Ikkan-kai, a Hōki-ryū group in Kyoto, offers a map (in Japanese) indicating all the samurai domains that taught Hōki-ryū during the Tokugawa Period. While most locations were in Western Japan, a number of them were located in Eastern Japan.