Houston's metropolitan rate of expansion has increased 19.8% since 1970, bulking us up by 393 square miles in the 2000s alone. That makes Houston the 12th-fastest-growing metro in the last four decades, and is contributing to Houston's affordability. Analysis by BuildZoom reveals that the majority of US cities have maintained a constant pace outward since the 1950s. But some of America's biggest cities have slowed their growth (BuildZoom calls these "expensive" cities), which is sparking growth in other, "expansive," markets.

BuildZoom's chief economist, Dr. Issi Romem, explains that America's largest ("expensive") cities like San Francisco and Boston channeled economic growth into higher properties values rather than outward expansion. They failed to compensate with densification and didn't build enough new housing. That affects the nature of who can and cannot afford to live there. The result, he says, is a middle-class exodus that fuels population growth in other cities that are growing, the "expansive" cities like Houston.