What We're Measuring

Below are four different maps of a 117 lot residential area in Marlborough, CT pictured to the left. Each accurately measures “developed” land correctly, but using different techniques that arrive at very different results. Building footprints and roads, except in the “Planimetric” map to the left, are used for reference only.

"Planimetric" map	Remote sensing derived land cover map

10% developed	30% developed
Technique: Created from digitizing aerial photographs, showing outlines of houses, driveways, roads and outbuildings.	Technique: Land cover depicted as 30 meter (~100 ft per side) pixels representing predominant reflective signature of each pixel.
Possible uses: An accurate way of determining the amount of impervious surfaces for runoff modeling, estimating impacts on water resources.	Possible uses: Good for town, regional or statewide planning purposes. Generally shows what is on the land within the limits of the resolution of the data.
Generalized land cover map	Parcel map

82% developed	100% developed
Technique: Developed area drawn by hand around developed areas as “eyeballed” from planimetric, aerial photo, ground survey or other type of image.	Technique: Parcel (property boundary) data depicted as “developed” if a structure is on it or if it can not be used for residential use (e.g. it’s all wetlands, open space set aside, etc.)
Possible uses: Common type of map seen in town plans. Good for general planning purposes but highly subjective.	Possible uses: Shows land that is currently or potentially committed to developed uses. Good for build-out analyses or to identify developed vs. developable land.