Past and Future of Vermont’s Imagery Program
Vermont has experienced significant changes across its landscape since the onset of European settlement, the impacts of which early environmentalist and VT-born George Perkins Marsh clearly understood. Cartographers, surveyors, photographers, writers and artists have captured much of this history in their works. More specifically, geographers and land use planners have looked to the past to help inform the future.
Maps have been an important tool in human history, serving as useful representations enabled by evolving technologies. Pigeons, balloons, kites, and eventually airplanes gave mapmakers a new vantage point, enabling the systematic acquisition of aerial photography. These advances led to a revolution in mapmaking. State and Federal agencies embraced this new technology in the 20th century, commissioning the acquisition of aerial photography, including projects in Vermont during the 1930s, 1940s, and 1960s.
Advances in technology eventually supported the production of orthophotos; photos that have properties of a map, having been adjusted for camera tilt, lens distortion, and topographic relief. Vermont’s Mapping Program (VMP), established in 1968 under the Department of Taxes, was charged with using such technology for the acquisition and distribution of leaf-off orthophotos. VMP’s orthophotos became the standard for 1:5,000 and 1:1,250 scale leaf-off orthophotographs in Vermont (Figure 1).
Beginning in the 1990’s, newly acquired analog orthophotos were digitized and converted into raster images and distributed on CD-ROM disks. In 2008 the orthophoto program was transferred from the Department of Taxes to the Vermont Center for Geographic Information (VCGI), establishing VCGI’s Imagery Program (herein referred to as the Program). VCGI switched to acquiring color leaf-off digital orthoimagery in 2011, captured at 50cm ground sample distance (GSD), including the near-infrared band. As of 2016, all imagery is now captured at 30cm GSD, with downtowns and villages captured at 15cm GSD. All of Vermont’s orthoimagery is in the public domain and freely available to all as downloadable files and streaming web map services.
As 2020 approaches, VCGI and the State’s Enterprise GIS Consortium (EGC) are working to evaluate the Program. An Orthoimagery Workgroup has been chartered and tasked with developing recommendations for the future of the Program. The Workgroup has been asked to evaluate the following questions.
1. Should the Program continue to produce custom products that are available in the public domain? The Vermont Mapping Program (VMP) charged fees for their orthophotos, prints (mylar/paper) and later digital files on CD-ROM. Orthophotos were exempted from Vermont’s public record law, meaning VMP could set a price beyond the “cost of recovery” as stipulated in public record law. The goal was to generate revenue to help support VMP’s efforts. When VCGI inherited the VMP’s program it chose to make all digital files freely available for download. VCGI eventually worked with the Legislature the remove the public record exemption for orthoimagery, meaning that the State’s orthos are now classified as a public record. What happens if the Program chooses to procure licensed imagery? Other states have moved in this direction, including Massachusetts and Utah. Should Vermont do the same (which could constrain access to only those who fall under the license agreement)?
2. Is leaf-off imagery still a critical requirement? Is leaf-on acceptable? Vermont’s orthoimagery has always been acquired during the spring while the leaves are still off the trees and after the winter snow has melted away. Leaf-off imagery (see Figure 3) enhances the visibility of features under the tree canopy, which is critical for many mapping and surveying applications. However, it limits acquisition to a narrow window in the spring, complicating and increasing the cost of acquisition. Licensed imagery providers cannot guarantee leaf-off imagery, which could eliminate the licensing option if leaf-off imagery is considered “critical” by key Program stakeholders.
3. Do we need higher resolution imagery? During the last acquisition cycle the Program has acquired imagery at a 30-centimeter ground sample distance (GSD) statewide, 15-centimeters in downtowns/villages (paid for by VIP) and all of Chittenden County (paid for by CCRPC and its member towns). Is this adequate? Can higher resolutions be justified given the additional cost?
The Orthoimagery Workgroup has its first meeting in August 2019. They will begin to grapple with these and other Program related questions, with the goal of having recommendations by the end of the year. VCGI will use the Workgroup’s recommendations to guide the requirements specified in a Request for Proposals (RFP) for the procurement of new orthoimagery, the first step toward the next vintage of Vermont orthophotos.
What do you think? You can help by completing this survey. Thank you.
Steve Sharp, GIS Operations Manager
VT Center for Geographic Information
