Apart from the radiation map of Ministry of Education, Culture, Sports, Science and Technology, the international team of USRA, Nagoya university, and Tokyo university simulated the spreading of cesium-137 from 3/20~4/20.
Though there are some questions, such as why it’s from 3/20, not 3/11, and it has already happened so, it’s not even a “simulation”, they calculated the whole amount of cesium-137 which fell on Japanese island from 3/20 to 4/20 is only 1,000 Tera Bq or a bit more.
They stated it spread out to western Japan and Hokkaido too because of the storms.
There is nowhere to escape in Japan.
The video below is when a person measured radiation at the furthest and remote northern point in Hokkaido, Soya misaki.
The counter showed 0.431 micro Sv/h at the maximum. It might have been affected by granite, but actually even when the counter is in the air, it showed about 0.14 micro Sv/h, which is as high as in Tokyo.
The reporter guesses it might be because of the tourist to take to plume on their shoes.