Greening the National Map: a new feature allows this compilation of country-wide geographic data to show communities just how their land cover is changing

American Forests, Spring, 2005 by Gary Moll

The memory of September 11 brings to mind images of tragedy and concerns about national security. But in some parts of the government it was a wake-up call for the necessity of an easily accessible base set of geographic data on the whole country.

Having that information in the public domain, it was felt, would make it easier for agencies and organizations to act quickly in a crisis. That need is being fulfilled with a computerized map that allows viewers to home in on a particular place and download relevant features.

Welcome to the aptly named National Map. Maintained by the U.S. Geological Survey, it debuted on the web in 2001; information is being added constantly.

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Federal, state, and local governments depend on a shared base of information that describes the earth's surface and locates features to accomplish a wide range of actions. In an extreme case--a crisis like 9/11, for example--it is hoped the map would serve as a collection point for up-to-date information.

A SHARED RESOURCE

This shared information, also used by private industry, nonprofits, and individual citizens, provides the centerpiece for economic and community development and land use, and now measures natural capital ecosystem services.

"The National Map is designed to provide public access to high-quality, geospatial data and information to help inform decision making," says Paul Hearn, a senior scientist in the U.S. Geological Survey's Geography Discipline. The map is growing constantly, and includes data not only from USGS but also from a large number of USGS partners at the local, state, and federal level. Think of it like a giant warehouse filled with geographic data; users select the data that meets their individual needs. One of the map's layers offers a look at land cover--a view of trees and other vegetation as well as built surfaces--buildings, sidewalks, parking lots.

"The information, currently based on satellite imagery from 1992 and 2001, is expected to be especially helpful in addressing land-management issues," says Nick Van Driel, chief scientist for information sciences at the USGS's National Center for Earth Resources Observation and Science.

The National Land Cover Database (NLCD) "has been mapped by conducting a nationwide land cover classification of Landsat satellite imagery," Van Driel adds.

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One fact that satellite data will show is the alarming rate of tree loss around urban areas. To help cities combat that trend, AMERICAN FORESTS has joined with USGS to provide information that will help cities evaluate their urban forest ecosystem as a working, physical asset and better integrate development plans with sound green infrastructure policies.

DECADES OF TREE LOSS STUDIED

AMERICAN FORESTS first began championing urban forests in 1981; in the years since, the organization has analyzed satellite imagery and recorded decades of trees lost to urbanization. Its effort to understand urban forest ecosystems shifted into high gear in 1991, fueled by support from the U.S. Forest Service and guided by a steering committee comprised of experts from diverse fields ranging from the environment to remote sensing.

In doing so, AMERICAN FORESTS studied the structure, function, and value of urban forests. The findings were clear, although some ran counter to popular belief. Most people thought of urban forests as street trees, but the organization found that 90 percent of the trees in an urban forest ecosystem were on private property or in yards or open space.

AMERICAN FORESTS also found that it was possible to measure the dollar value of the work performed by an urban ecosystem in cleaning the air and water; AMERICAN FORESTS calls this work "ecosystem services."

Determining those dollar values was important because it could be recorded on a budget sheet--and gave trees tangible meaning to city officials responsible for the fiscal bottom line Suddenly, tree value could be measured and included as a line item right along with schools, road salt, and police cars.

AMERICAN FORESTS has found only one technical system capable of measuring and modeling urban ecology--computer-based Geographic Information Systems. AMERICAN FORESTS developed a technique for calculating the value of nature in urban forests, which the organization called an Urban Ecosystem Analysis (UEA). In the mid-1990s AMERICAN FORESTS conducted a couple dozen UEAs and documented the decline of urban forest ecosystems and the costly impact it had on communities.

CALCULATING THE URBAN TREE DEFICIT

In 2001 AMERICAN FORESTS measured the nation's tree cover and calculated the United States has an "urban tree deficit" of more than 634 million trees. From the late 1980s to the late 1990s, unplanned growth in major metropolitan areas increased by at least 20 percent, more in some places.

The partnership between USGS and AMERICAN FORESTS takes the national map to the next level. The National Map's National Land Cover Data set can display land cover at multiple scales, as shown in the image on page 41. There, the large view shows data from coast to coast. Smaller windows show the East has heavy tree cover but the Southwest does not. For more detail, it's possible to zoom in on a particular state, county, or even small city such as Leesburg, Virginia.