The City of Ann Arbor, Michigan contracted Sanborn to produce an impervious surface map created from 6-inch resolution orthophotography. The impervious surface map was produced in order to help make the city’s tax assessment processes more equitable by allowing accurate calculation of the amount of water runoff from a parcel and to calculate the parcel’s impact on the city’s stormwater system.

Project Scope

The impervious surfaces were delineated using automated methods, and the output was manually edited to produce Sanborn’s Premium Impervious product. Water was delineated as a separate class, making the resulting output a three-class product. The imagery was flown in the spring, prior to leaf-out, making possible the accurate delineation of impervious surfaces below the tree canopy.

The end use of this product was as a base for taxation, so the data was required to meet an accuracy standard that would stand up to legal challenges. The Sanborn Premium Product is designed to meet those standards while greatly reducing the costs involved in producing a traditional planimetric dataset. Once the impervious delineation was complete, the dataset was correlated with the parcel database for the City of Ann Arbor and included in the city’s taxation database.

Impervious Surface Calculation

Technical Specifications

Products Produced: Premium Impervious
Imagery Used: Color Infrared Imagery
Classification Approach: Automated Classification with Manual editing
Accuracy Assessment: Exceeded 95%
GIS database development and management: Delivered in geodatabase
Documentation of geospatial analysis methods and metadata: Metadata provided

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