Connecticut Statewide Impervious Surface Map Layers

By Emily Wilson

Originally published by the UConn Center for Land Use Education and Research

impervious surface map layer in ESRIWith funding from CT DEEP, CLEAR has acquired and made available on CT ECO a new statewide, high-resolution, impervious cover data layer. While acquired to support new stormwater regulations, the layer can be used for other purposes as well.

What is it?

Statewide, 1 foot resolution raster (pixel) data where each pixel is one of three classes (buildings, roads and other impervious).

Why do we have it?

The 2017 Municipal Separate Storm Sewer System (MS4) General Permit regulation requires certain towns and institutions to calculate directly connected impervious area. To assist communities in meeting this requirement, CT DEEP funded the acquisition of the a statewide impervious layer (based on 2012 imagery) that may be useful in calculating directly connected impervious area and tracking disconnects of impervious cover.

How was it created?

A company called Quantum Spatial did the work.  They used 2012 statewide aerial imagery which has 1 foot pixels and classified it which means identifying all pixels in the imagery that represent buildings, roads and other impervious.  The rest of the pixels were excluded as they were not impervious land cover. In some places, towns and/or regional governments contributed detailed GIS data that was incorporated into the layer.

How do you get it?

The CT ECO website has a whole section devoted to the Connecticut MS4 Supporting Layers which includes the impervious surface data.

View. Take a quick peak at the layer. Or view it in context in the CT MS4 Viewer (look for Statewide Impervious Cover (2012) down a ways on the Layer List).

Connect. GIS users can connect to the map services of impervious surface. Three flavors are available.

The original raster data is available as map services in two different projections. One is in Web Mercator Auxiliary Sphere (service called Impervious_2012) which is best for online mapping and web viewers.  The other is in Connecticut State Plane NAD83 Feet which is better for desktop GIS mapping when other layers are also in the Connecticut State Plane coordinate system (service called Impervious_2012_StatePlane).  The smoothed vector version (see formats section below) is also a map service in Connecticut State Plane NAD83 feet (service called Impervious2012_simplified_vector_StatePlane).

Download. GIS users can download the files.  Formats available described below.

What are the different formats?

The impervious surface data is available in several different flavors that all originated from the same base.

Raster.  The raster format is the original. Download by town (extended area*).

Vector Original. The vector format was created by taking the raster layer and converting it to polygons instead of pixels.  Polygons have area. Here, the polygon edges are still jagged because they originated from pixels. The outlines are shown as an example. Download by town in a geodatabase contain a clip of just the town boundary and one of the town extended area*.

Vector Smoothed. Through a fortunate turn of events, there is also a smoothed version of the vector. Here, the jagged vectors have been smoothed through geoprocessing methods. Download statewide layers for buildings, roads and other impervious.  Each is in a separate file.

* Extended area refers to a rectangular area larger than the town (detailed explanation here).

Telling Stories with Maps

map imageEmily Wilson wrote a blog post for Map@Syst on the story maps being created by UConn Extension:

CLEAR’s Extension faculty have long used maps to educate land use decision makers and the public about Connecticut’s landscape and natural resources.  The Connecticut’s Changing Landscape (CCL) research project has been the foundation of the education.  CCL is a series of satellite-derived land cover maps for six dates between 1985 and 2010 (2105 is coming soon) that includes 12 classes such as development, turf, agricultural field and forest.

Although the CCL website has evolved with time and technology, it has always strived to integrate the graphic, quantitative and geospatial information in easy to access ways – virtually the same MO of the Story Map.  Story maps easily integrate text, multi-media like photos and video, graphics and of course, interactive maps in one, contained interface.

CLEAR’s extension faculty were energized and began to implement loads of CCL information into CLEAR’s first Story Map – Connecticut’s Changing Landscape.  It is an ideal way to boil down the inherently complex information including combinations of land cover categories, time intervals, derivatives and scales.

Read more…

Did You Know: Mapping the Industry


shellfish mapShellfish aquaculture is a large and growing part of Connecticut’s agriculture sector, but site selection is a major challenge. Farmers cultivate oysters, clams and scallops in designated areas of Long Island Sound. Those sites are considered public property and are leased from the state. Farmers need to identify growing areas that are biologically productive for their crop while also considering the potential use conflicts or environmental interactions with their activity on those sites.

To help improve site selection for aquaculture, the Aquaculture Mapping Atlas was developed by Assistant Extension Educator Cary Chadwick, in collaboration with Extension Educator Tessa Getchis and the Connecticut Department of Agriculture, Bureau of Aquaculture.

The latest version of this interactive map viewer includes new data layers and functions. The viewer has updated commercial and recreational harvest areas, natural beds, and shellfish classification areas as well as a plethora of navigation, environmental condition, and natural resource data. Users can overlay map layers, draw new lease areas, and print professional-looking maps.

Did You Know: Drones at Work

Mapping Great Gull Island with an Unmanned Aircraft

Joel and droneAssistant Extension Educator Joel Stocker spends a lot of his work and personal time documenting changes to the shoreline. In 2010 he contacted Helen Hays, asking if he could capture photographs over Great Gull Island with his homemade drone. She agreed. While on the island, Helen told him about the problem with invasive plants, and he connected her with Juliana Barrett.

Recognizing high-resolution aerials could be used to monitor vegetation management Juliana included experiments with aerial drone flights as part of a Connecticut Sea Grant proposal. In April 2013 the official Extension/Sea Grant flights took place, fully sanctioned by the FAA. Over 370 photographs were captured from a small four prop multirotor quadcopter, later processed using two different software systems, AgiSoft Photoscan and Pix4Dmapper. The result is a full high-resolution orthomosaic image of the entire island – a detailed tool for the habitat management plan. In addition the Pix4D software produced a full 3D topographic map, great potential for measuring erosion and the before and after effects of natural disasters like Superstorm Sandy.

Dealing in Imagery

By Emily Wilson


My extra desk has seen a steady stream of boxes – little and big ones, brown and black ones, even an iPad box (no iPad included).  One had old maps crumpled up to protect its contents.  Some have been dropped off and others have been part of a suspicious looking package trade at meetings across the state.  But they all contain the same thing – an external hard drive, cleared and prepared for all 571 gigabytes of Connecticut’s new aerial imagery.  Who do these boxes belong to? It is a wide range – private firms, federal agencies, utility companies, universities and municipalities to name a few.  And equally as diverse are the applications.  Mapping professionals use the imagery as background in maps and map viewers, to find and map roads, manholes, utility poles and other infrastructure, to find and map natural features like vernal pools, streams, vegetation and trees, and to detect changes on the land by comparing to older imagery.

But the imagery is not just for mapping professionals.  On CT ECO (a partnership between UConn CLEAR and CT DEEP), we provide the imagery in a range of ways to meet (almost) any level of technical ability. The simplest way is the map catalog, where you will find two pdfs for each town – one true color and one color infrared.  Just slightly more involved are the thematic map viewers where you can add other data layers or compare to older imagery.  The sophisticated user can connect to the map services in GIS software or ArcGIS Online.  And finally, for those mappers who want the actual data but haven’t brought your hard drive to me for the big copy, you can download the imagery as GeoTIFF tiles, MrSID tiles or town mosaics.

The download option is a first for CT ECO and for Connecticut and we are excited about it. It should make for easy and fast imagery access and will likely slow the drive trafficking in my office (and offices at DESPP, DOT and DEEP too).

Check out the imagery on CT ECO and, as always, let us know what you think.  And, by the way, boxes of chocolate, as well as hard drives, are always welcome.

More information and links to all the ways to view the 2012 Imagery on CT ECO