How Urban Planners Use Landsat and the National Land Cover Database

"A vision to observe Earth for the benefit of all…" — Interior Secretary Stewart Udall, 1966

Agencies managing the growth of cities are looking more and more to the sky.

• A world of cities: in 1960, more than 1 billion people lived in cities; by 2019, nearly 4 billion.
• The U.S.: 8 in 10 people live in cities on roughly 4 percent of the land — a small share, but growing, with long-term effects.
• The questions: what happens to woodland plants and animals when forest becomes dense urban cover? Where does rain go when farms and fields are paved into parking lots? Feeding, housing and powering cities draws on rural resources, changing land far beyond city limits.

Landsat satellites can help answer them.

National Land Cover Database images of southeastern Phoenix, 2001 and 2011: suburbs (red) spread through Mesa, Gilbert, Chandler and Apache Junction, and Maricopa appears at lower left. USGS.

A long record

Other satellites have imaged cities for 10 to 15 years; Landsat has watched urban change worldwide for 47 years, notes Collin Homer, land characterization project chief at the USGS Earth Resources Observation and Science (EROS) Center. Its mid-level resolution captures urban growth over far wider areas than finer-resolution satellites.

The National Land Cover Database

That repeat coverage built the National Land Cover Database (NLCD):

• Editions: 2001, 2006, 2011 and 2016, released every 5 years — and now annual land-cover and land-change products through EROS's LCMAP initiative (Land Change Monitoring, Assessment, and Projection).
• Detail: the lower 48 states mapped in cells 98 feet on a side, each assigned one of up to 16 classes under natural vegetation, agriculture and urban.
• Layers: tree canopy cover, cropland, and the percentage of impervious surface — asphalt, concrete, rooftops.

What it's used for

• Runoff and flooding: paved land can't absorb rain, which runs off streets, lots and roofs and pools in low spots, raising flood risk — and carries chemicals from pavement into rivers and ecosystems downstream.
• Wildlife and disease: NLCD shows how growth affects wildlife at the urban fringe, and helps model the paths of diseases carried by ticks, mice and mosquitoes — where they live and how they cross a city to reach habitat.
• Livability: urban geographers use it to gauge quality of life — from the number of parks to housing density. The U.S. Census Bureau has formally adopted the NLCD impervious layer to better understand where people live.
• Beyond federal agencies: state governments, natural resource offices and others rely on Landsat and the NLCD too.

Sources

Based on Urban Planners and Urban Geographers Turn to Landsat for Answers, U.S. Geological Survey Fact Sheet 2016–3056, version 1.1, September 2019 (publication page), Earth Resources Observation and Science (EROS) Center. Its opening and the Phoenix images are restored from the fact sheet's PDF. A work of the United States government in the public domain.