Cities sit unmoving on the landscape — a sprawling collection of roads, sidewalks, and buildings designed to last for generations. But across the United States, urban areas are silently shifting: The land beneath them is sinking, a process known as subsidence, largely because people are using too much groundwater and aquifers are collapsing. The sheer weight of a metropolis, too, compacts the underlying soil.

A new study published on Thursday in the journal Nature Cities mapped the scale of this slow-motion crisis across the country. Researchers used satellites to measure how the elevation has been changing in America’s 28 most populous cities — including New York, Dallas, and Seattle — and found that in every one of them, at least 20 percent of the urban area is sinking. In 25 cities, two-thirds or more of the area is subsiding, with rates up to 0.4 inches each year.

Groundwater withdrawal was responsible for 80 percent of total subsidence in the cities. As urban areas grow — and as climate change exacerbates droughts, especially in the American West — their people and industries demand more water. Overall, the study found that across the 28 cities, nearly 7,000 square miles of land is subsiding, threatening 29,000 buildings and potentially affecting 34 million people. Hot spots include Los Angeles, Las Vegas, San Francisco, and Washington, D.C.