Answer: About 8 out of 10 people live on limited flat land near the ocean.
Explanation:
Looking at Japan's terrain will show one very glaring fact, it is dominated by mountains.
Japan's terrain is over 70% mountainous and so very hard to live or construct on. The remaining flatter land is around the coasts so that is where the majority of the population choose to stay in. That way they can build stable buildings and do other useful things is in this very limited useful piece of land.
