Plant by Numbers
New digital mapping technology driving urban reforestation efforts.
Digital mapping shows tree canopy coverage in New York's Central Park and Columbus Circle.
Courtesy Spatial Analysis Laboratory

Cities across the country are increasingly adopting data-driven approaches to establishing goals and priorities for large-scale tree restoration projects. This approach is made possible by new technologies that provide a detailed look at the urban tree canopy (UTC), or the layer of leaves, branches, and stems of trees that cover the ground when viewed from above.

Researchers at the University of Vermont’s Spatial Analysis Lab and the USDA Forest Service’s Northern Research Station are working with cities to leverage existing terrain data gathered using LiDAR (light detection and ranging) technology in order to assess tree canopies. This LiDAR technology allows for an accuracy not provided by aerial and satellite images in which trees are frequently obscured by building shadows. In a LiDAR survey, the system is mounted on an aircraft and sensors emit a laser light (5,000 to 50,000 pulses per second). The result is three-dimensional visualizations of data that can then be integrated into GIS for analysis.


“The data goes beyond determining the amount of tree canopy,” says Jarlath O’Neil-Dunne, Director of the Spatial Analysis Lab. These maps are overlaid with census reports, demographics, property records, and other datasets that allow cities and not-for-profits to prioritize tree-planting efforts and tree maintenance plans, but also to understand patterns of environmental justice and to justify budget increases for urban forestry programs.

Cities like New York, Pittsburgh, Baltimore, and Washington, D.C. are using LiDAR data to inform tree-planting initiatives. In 2010, New York City funded LiDAR data collection to map the city’s tree canopy and prioritize the goals of the MillionTreesNYC initiative.

The non-profit organization Tree Pittsburgh is using the urban tree canopy data to not only prioritize tree-plantings, but to also begin to address larger urban issues, such as economic justice and the challenge of shrinking cities. “A lot can be learned overlaying tree canopy data with other datasets,” said Danielle Crumrine, director of Tree Pittsburgh. Crumrine’s organization is using the data to focus tree-planting efforts near senior centers and schools in areas suffering from the urban heat island effect. “We would love to overlay asthma and obesity rates,” Crumrine said. Pittsburgh’s urban tree canopy maps are also being used to address long-term planning issues. The city is “thinking about how to connect vacant land to existing Greenways,” said Crumrine.

Liz McEnaney