ISGIS: Impervious Surface GIS

Project Title
Impervious Surface GIS

Time Span
2002 - 2003

Summary
The City and County of Denver Colorado established a storm drainage utility over twenty years ago. The utility assesses a fee on all properties in Denver based on the amount of impervious surface present on each property, as well as on the percentage of the total area of each property that the impervious surface represents. Though Denver employed GIS technology to digitize the required data over a decade ago, it reverted to measuring surfaces manually in the field, an inefficient process.

In 2002, Denver hired NSG team members to implement its Impervious Surface GIS (ISGIS) for the County. The system was implemented using ArcGIS and a personal geodatabase, requiring only licenses of ArcView to be used. The system builds on the ArcMap component of ArcGIS, both removing unnecessary toolbars from the user interface and adding several custom toolbars. The system simplifies the interaction with the software to the point that field inspectors who once spent many hours measuring impervious surfaces in the field now spend a few minutes on each parcel measuring it on the computer. Following the initial implementation, the NSG team upgraded the system to work with an ArcSDE geodatabase, complete with versioning and multi-user editing. The NSG team then tied ISGIS into the stormwater billing system for rapid database update, allowing Denver to collect over $12,000,000 annually in impervious surface fees and be a leader in the implementation of GIS for the support of a stormwater utility.

Technologies

• ArcSDE
• ArcGIS
• ArcObjects
• Oracle

Innovations

• Digitize impervious surfaces from orthophotographs, scanned site plans, and parcel maps
• Georeference site plans and parcels to orthophotographs
• Integrate with billing system
• Simplify ArcMap interface
• Receive rapid buy-in from field staff
• Increase accuracy, defensibility, efficiency, and speed