Take a trip out on the London Underground’s Metropolitan Line and you soon find yourself passing through neighborhoods of semi-detached and detached houses with gardens, giving way on occasion to green fields. In Paris or Tokyo, you’d be far more likely to be looking out on apartment blocks of three to six stories. The preponderance of low-rise single-family homes close to train lines and within cities is what gives Britain’s landscape its distinctive character. It’s also a factor in one of the