Impervious Surface

Impervious surfaces, defined by Wikipedia as mainly artificial structures—such as pavements (roads, sidewalks, driveways and parking lots, as well as industrial areas such as airports, ports and logistics and distribution centres, all of which use considerable paved areas) that are covered by impenetrable materials such as asphalt, concrete, brick, stone—and rooftops. Soils compacted by urban development are also highly impervious.
Impervious surfaces generate runoff that creates increased flooding, erosion, and water pollution issues for urban communities and their surrounding environments. Further, combined sanitary and storm water sewer systems currently used in many older cities result in greater pollution and environmental degradation. Knowing the extent of a community’s impervious surfaces can help to locate areas that may benefit from Best Management Practices (source: Sanborn). 
For entities interested in purchasing an impervious surface layer through NCTCOG, the chosen consultant will create the layer(s) using orthophotography, 0.5m LiDAR and parcel data (if available). 

  • The following specifications are based on source imagery captured at a scale of1:1200 and containing a pixel resolution of 0.5'.

  • Minimum Mapping Unit (MMU) of 100 sq. ft. (MMU is a target unit; some polygons captured as part of an impervious data layer might be less than 100 sq. ft.)

  • Sidewalks 5' or greater in width should be captured (with imagery resolution of 0.5').

  • Circular portions of polygons should be captured so that the feature appears to be circular when viewed at a scale of 1:1200.

  • All adjacent impervious polygons should be merged to form a single impervious polygon.

  • Attempts should be made to fully captured features hidden by tree canopy, building shadow, or other obstacle by interpolating portions of hidden impervious surface areas.

  • All features captured are based on aerial imagery interpretation. Field visits are not typically used to delineate impervious features.

Data Dictionary

Surface Type  Surface Description
1 Existing Paving
2 Existing Gravel
3 Alley with Paving
4 Alley without Paving
5 Median
6 Asphalt Path
7 Concrete Pad
8 Hard Packed Gravel
9 Park
10 Parking Lot
11 Patio
12 Private Street
13 Misc
14 Sidewalk
15 Building
16 Railroad Hard Packed Gravel
17 Driveway
18 Existing Paving Bridge
19 Sidewalk Bridge
20 Pool

The scope of any Impervious Surface mapping project is dependent upon the needs of that year’s participating entities.

Sample Impervious Surface File (coming soon)

For more information about impervious surface mapping, contact Shelley Broyles at 817-695-9156 or via email.