Japanese think Japan is a tiny country but the fact is not. Honshu island is 7th largest island in the world and area bigger than Japan in Europe(excluding Russia) is just France, Spain and Sweden. However, the population is much more than these three nations and the 60% of the land is mountainous which means not ideal place to live.
Therefore many people must live in two stories or higher apartments in big cities. Apartments are divided into 3 categories. First one is called APART which is a smaller flat which is on the rent basis. The second one is called MANSION which is bigger, taller flat which each unit is owned by each landlord and the third one is DANCHI. Danchi is a large cluster of buildings typically built as public housings.
Danchi and mansion were built in the suburbs of the big cities but recently high rise mansion are built in bay area of Tokyo rather than in the suburbs. These buildings are built according to strict architect laws against earthquakes and recent buildings are not earthquake-resistant structures but seismic base isolation.