Each block of land in Japan has two ratios called "Yosekiritsu" and "Kenpeiritsu" which set the limit for the total size of the house and the size of the footprint of the house on the land.
Yosekiritsu is the total volume or size of the house in relation to the land. It is expressed in percentage terms.
Kenpeiritsu is the building to land coverage ratio.
Land in central Tokyo generally has higher ratios than land in outer areas such as Setagaya or Denenchofu. Land in a Category 1 and 2 Low-rise Exclusive Residential District will typically have low ratios, making such areas desirable as they are not as densely crowded.
There may also be laws that designate how close your house is allowed to be built to the boundary. A wider distance is good if you don't want to hear your neighbours snore or shower, but it will also restrict the size of your home.
In Japan, houses are low buildings that must be separated, so that in case of earthquake do not hit each other.
Manuel Pinar. Tokyo 2015