Planimetrics: Aerial data to support regional planning

When creating digital plans, it’s essential to have an accurate representation of the natural and built environment. But how do you achieve that?

These representations of our landscape aren’t just developed on a computer screen—they are digitized versions of the real-world environment of the region. Planimetric data are digital points, lines and polygons representing features on the ground, such as manholes, coastal infrastructure and catch basins, that can be used in geographic information system mapping applications.

To generate planimetric data, aerial surveys are conducted periodically to collect orthophotography, which is then analyzed and digitized to construct a virtual world that planners can use. Orthophotography refers to a process that captures aerial photographs or satellite imagery, producing geometrically accurate, map-like image with a uniform scale, enabling precise measurements and analysis.

Generating these images isn’t as simple as flying over the region on any given day. The conditions must be just right. Aerial photographs need to be taken at the optimal time of day to minimize shadows, with clear skies, no leaves on the trees, and at low tide to ensure maximum visibility.

Once captured, the images are sent to a contractor who analyzes the data, identifying and mapping key features such as park benches, fire hydrants, pavement markings, curb cuts, buildings, and trees. These elements are digitized as points, lines, and polygons to build an accurate digital representation of both the natural and built environment.

The Cape Cod Commission plays a lead role in overseeing this project and analyzing the data, which is then distributed to all 15 towns for use by planners and other local officials in their development and planning efforts.

The region’s first coordinated aerial survey took place in 2014, using stereo pairs to support a comprehensive planimetric mapping effort. An upcoming planned flight will be the third regional survey in the past decade, following data collections in 2014 and 2020. With this multi-year dataset, planners, engineers, assessors, analysts, and even the general public can better track changes over time—tracking miles of sidewalks, new developments, and other transformations at various scales, from neighborhoods and villages to entire towns and subregions.

One of the most exciting aspects of this data collection is monitoring changes in the built environment, where development and infrastructure evolve over time. Street trees, for example, are recorded as point features with height attributes, and species data could be attached for further analysis. Cape Cod also tracks two unique features not commonly included in standard mapping efforts: tree canopy and landscape area. Tree canopy represents overhead coverage, while landscape area distinguishes between managed natural spaces—such as lawns, shrubs, and meadows—and unmanaged natural areas.

The third flight will take place this spring, with updated planimetrics data anticipated by the end of the year.