2012 Impervious Surface Download

The 2017 Municipal Separate Storm Sewer System (MS4) General Permit regulation includes several mapping requirements. New and existing statewide data layers are compiled here to assist municipalities and institutions in complying with the permit requirements.

CT DEEP has funded the acquisition of a new statewide impervious layer (based on 2012 imagery) that may be useful in calculating directly connected impervious area and tracking disconnects of impervious cover. UConn CLEAR has used this data to create both an impervious cover by basin and an impervious cover by town layer. The 1 foot resolution data contains three classes (buildings, roads and other impervious).

UConn CLEAR has also created an impaired waters layer that highlights only stormwater related impairments.

For more information, visit the MS4 website at NEMO or email nemo@uconn.edu.

All files are in Connecticut State Plane NAD83 feet.

Town Download

Click on a town on the map (right) and then choose to download vector or raster versions of the impervious surface.

 Map Services

The 2012 Impervious Service map services (in the Built category) may be easier to use depending on your application.

State Download

The statewide raster was converted to vector format, simplified and then divided into three layers - buildings, roads and other impervious. See next section.

Statewide Impervious Cover Vectors

The statewide impervious layers (below) are a variation of the rest of the 2012 impervious available. The layers have been smoothed and simplified in order to remove the "pixelated" look and to reduce file size.

 Download statewide 2012 buildings, shapefile format, 210Mb. The layer shows where buildings are but does NOT contain any other information like address or building type.

Download statewide 2012 roads, shapefile format, 29Mb. These are polygon roads meant to show where impervious surface exists. The layer does NOT contain road names, number, length or any other supplementary information.

Download statewide 2012 other impervious, shapefile format, 342Mb. "Other impervious" includes parking lots, sidewalks, driveways, patios, swimming pools and decks. That being said, there is no distinction between these features in the layer.


How is the statewide dataset different from the others?

 The graphics show it best. The lines show the edges of the statewide layers solid colors are the raster shapes and the outlines are the layers after they have been processed.

The original layers in town vector and raster formats

The smoothed statewide vector dataset

Combining the two for comparisons sake. The statewide layers are the outlines (purple=buildings, red=roads, orange=other).


The impervious layers are available in both raster and vector format. A raster is comprised of pixels and a vector is comprised of points, lines or polygons. The impervious layers here are all polygon layers meaning that they contain shapes that have area.

The raster layer is in img format and has 1 foot pixels with three classes (1=buildings, 2=roads and 3=other impervious). It was derived from the 2012 statewide orthophotography.

The vector layers were created by converting the raster layer to polygons. Two vector layers exist in each town geodatabase. One is clipped to the town boundary. The other with buffer on the end of the file name, covers a rectangular area larger than the town boundary. The buffered areas were determined by including all tiles from the 2012 aerials that intersected a rectangular bounding box for each town. The buffer version is included for applications that benefit by looking across town boundaries.

Town Extended Area

Clipped to Town Boundary

There are two feature classes in each town geodatabase available for download. One feature class has the word buffer on the end and the other does not. The one without buffer on the end has been clipped to a town boundary as provided by CT DEEP.

Clipped to Town Extended Area

The feature class with the buffer on the end AND the img raster available for download both cover a larger area than the town.

1. Buffering the town boundary (black line) by 300 feet.

2. Overlaying the tile grid used for the 2012 aerial imagery (red lines).

3. Selecting all tiles (cyan) that intersect the 300 foot buffer area (yellow).

4. Adding more tiles to the selection (cyan) so that the area is a rectangle.

5. Using the extent of the selected tiles as the bounding box (orange) for clipping the 2012 impervious to the town extended area.