Cities around the world have expanded physically as they grow in population, with increases in their surface extent, with the creation of high-rise buildings for residential and commercial use, and with development underground.
As cidades ao redor do mundo expandíronse fisicamente ó tempo que medraban en poboación, con aumentos na súa extensión, coa creación de grandes edificios para uso residencial e comercial, e co desenvolvemento do metro.