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Data Evolution
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Validating your GIS with Network Analysis
These are just a few examples of the connectivity issues that need to be addressed prior to hydraulic modeling to ensure the data provided by the GIS is an accurate representation of real-world conditions.
Incorporating network analysis as a part of the QA/QC procedures will enable these additional connectivity issues to be identified and corrected. For example, if a bottleneck is identified in the GIS data set, the user must determine if the bottleneck is the result of inaccurate source information or if it is a legitimate design problem. If the problem is derived from incorrect source information, then the GIS facility layer can be updated with the correct pipe diameters. If the problem is a design problem, then the modeler can address it and determine what type of hydraulic impact this may have on the network. Identi$ing and correcting the connectivity issues ensure that the GIS data quality can support network analysis. In addition, other GIS applications will benefit. A few GIS applications that will benefit (they use the same connectivity rules used in hydraulic analysis) are: emergency valve shut down, cathodic protection and work-order design applications.
Facility Information
The second component in assessing data quality for modeling is the validity of the GIS facility information. Facility information is attribute data associated with each piece of equipment stored within the GIS. The validity of the facility information is a measure of how complete and accurate the information is. The validity of the data can be compromised during data conversion, the process of capturing source information from legacy data (paper maps, service cards). Data conversion focuses on ensuring that all critical information from the source documents are populated into the GIS database. The key is to have a one-to-one relationship between legacy data and the GIS database for all objects identified for conversion. This serves well in reproducing the current workflow processes that the legacy data once supported. However, since the legacy data was never designed to support network analysis, it is critical to identifi what additional information will be required to support these future GIS applications.
A few examples of missing hydraulic information required for network analysis are:
- Regulator Stations: Regulator stations are hydraulic structures which regulate pressure. The legacy data generally identifies the geographic location of these stations. However, performing network analysis requires specific information about the individual regulators within the station. Generally this information is either not stored in the GIS, or the information is limited in its content.
- Valves: Valves are devices which isolate or direct flow. These devices play a critical role in assessing the ability to control the pressure and flow of gas to customers. Generally, the GIS data will identifi the location of these devices and the associated pipe on which the valve is located. However, if valve information is missing or incorrect, the hydraulic results from network analysis will not reflect the true conditions in which the system is operating.
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