Nassau County Achieves Data Excellence from Diverse Sources

The Nassau County, New York, GIS is one of the most interactive local government systems in the nation. Along with its more than 343 users in 12 of the County's 55 departments, the County has a multiparticipant data sharing program with over 300 licensed partners. This includes a broad range of local, state, and federal agencies, as well as many private Businesses and organizations. Rather than being passive recipients of County-generated data, these users also contribute data as part of this unique multiparticipant GIS program.

All County-based users can access, enhance, contribute, and exchange data with the basemap and each other. In fact, one of the benefits of this program is that, as participants develop new products or enhance or correct existing data, a copy of the new or improved data is returned to the central database, providing an excellent mechanism for improving and strengthening the County's already large database. Multiparticipants currently exchange data through the use of CDs or electronic transfer via the County's FTP site. The County is now beginning a pilot project as part of a New York State (NYS) SARA/PEGI grant to enhance the ability of the multiparticipants to transfer data electronically.

It has been shown over and over again that a GIS is only as valuable as the data that resides in it. Nassau County is well known in the industry for its world-class, enterprisewide GIS solution because it recognized this important tenet at the very inception of the system and put into place appropriate mechanisms and safeguards.

Design

In the fall of 1990 when the project began, a very high priority was placed on understanding the needs of all potential participants and the very design of the system was based on those needs. Bowne Management Systems, Inc. (BMS), was commissioned by Nassau County to undertake a very detailed and exhaustive user needs assessment. More than 4,000 questionnaires were sent out. The questionnaire contained over 120 possible responses that when fully tabulated and cross-referenced, provided the County with a tremendous amount of information. Personal interviews with more than 330 users representing all 55 County departments then took place. The Bowne staff met with employees at sewer treatment plants, police precincts, maintenance garages, executive offices, airport hangars, and a host of other sites throughout the County. The final user needs assessment report became the basis for the conceptual design of the County's GIS.

Another important safeguard has guaranteed the accuracy and quality of the data collected. Because data is received from so many diverse sources as part of this multiparticipant program, Nassau County had to develop very rigorous quality acceptance criteria and adhere to them strictly. Doing so has guaranteed that all new data meets all standards before it is incorporated into the central database, thus increasing the confidence of all users in the reliability of the entire database.

Specifications

Among the foundations of the Nassau County project is the belief that documentation and detailed specifications are essential for data quality and successful projects, and that tolerances and tight specifications are critical. All data providers were directed to build quality into the data capture and acquisition process, with the goal of receiving correct data on the first delivery. This was a very different approach for most vendors.

Upon completion of the user needs assessment, an evaluation of commercial data sources, a review of trends in municipal GIS, and definition of the accuracy requirements of the County, it was determined that a photogrammetrically derived basemap was vital for the Nassau County project. The County developed a one-mile grid of over 600 survey markers or monuments using GPS, which provided the basis for the photogrammetric basemap that was subsequently developed. The resulting compilation consisted of 64 features divided into eight major categories including control features, hypsography, hydrography, vegetation, structures, transportation, utility features, recreation, and miscellaneous. Initially, this data was delivered in DGN format, as the final platform had not yet been chosen.

Bowne, the County's oversight vendor, worked with the various basemap data providers to make certain that their approach to quality control was effective. The source of all errors was determined, and the process was altered to prevent the same type of error from reoccurring. As the incoming data began to meet tolerable accuracy ranges, the County began to sample the data rather than performing a thorough review.

Software

As a result of a comprehensive proposal and evaluation process, Esri's ArcSDE, ArcInfo, and ArcView GIS were selected as the platform for this unique GIS. Since an extensive amount of data had already been created, migration of the existing data into the new system was an important first step. As part of the hardware and software acquisition, the County also contracted with Esri to take the existing land base data and several other boundary files and convert them for use in the new system. Additionally, Esri created an independent centerline file based on the edge of pavement data created as part of the photogrammetric land base project.

Cadastral Data

By the time Nassau County undertook the conversion of the parcel layer, they had experienced several other data development projects and had confirmed their belief that detailed specifications and acceptance criteria are keys to receiving a high-quality product on the first delivery. They had also learned that the vendor must be held accountable for the work they produce.

Nassau County selected Apex Data Services, an Esri Business Partner, as their conversion vendor for the cadastral project based on a competitive bidding process and its offer to deliver the highest quality parcel data at very competitive prices. The overall acceptance rate of the data delivered to the County was over 96 percent.

Infrastructure Data

Among the large data sets still being developed in Nassau County, infrastructure probably looms largest on the horizon. Tests to integrate DGN data from the NYS Department of Transportation and AutoCAD-based water distribution networks from a number of the water suppliers in the County have already been successfully completed. Other infrastructure data that has been loaded in test areas includes streetlights, drainage facilities, street signs, and signals, and other utility data such as gas, electric, and telecommunications facilities.

A pilot study completed two years ago demonstrated the technical and economic feasibility of converting the large quantities of sanitary sewer and other infrastructure data records within the County. Thus, as part of a project to upgrade the County's sewer maintenance system to a state-of-the-art GIS-enabled system, a contract has been awarded to scan, register, and digitize over 300 index sheets that define the 65,000 segments of the County's sanitary sewer network. In addition to the graphic features that define the sewer system, all identification information and attribute data from the drawings is being captured in the County's database files.

A set of detailed specifications and acceptance criteria will again be the basis used to ensure this next data collection endeavor is another success story for the County.

For more information, contact Joseph Jones, Nassau County (tel.: 516-571-4096, e-mail: jjones@nysnet.net).

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