Converting SUE CAD Files to GIS: A Perspective on Data Quality and Utility Records

Recently I posted an article about Utility Records Research (see article here), wherein questions were raised about SUE data management. A question that frequently arises relates to the integrity and quality of data when converting it from one format to another, particularly from CAD (Computer-Aided Design) to GIS (Geographic Information System). This issue is especially pertinent in the context of maintaining the reliability of utility records. A recent inquiry encapsulates this concern: "Does the quality level of a final drawing stamped by an engineer persist when the CAD file is converted to GIS for use in a municipal web GIS, or should those quality levels be removed since the stamp is no longer there?"

Understanding the Conversion from CAD to GIS

The process of converting a CAD file to GIS format inherently involves the loss of certain attributes and quality assignments made by the preceding professional. The quality levels, crucial in certifying the accuracy and reliability of the SUE data, are no longer applicable once the data enters the GIS environment. In this new format, the data is simply record information, devoid of its original quality certifications. This is not to say that the data has lost its value. The data remains inherently valuable, it does not however, retain its assigned quality levels.

Implications of Data Conversion

When utility data is transferred from a CAD to a GIS format, it essentially loses its certified quality status. This data cannot be classified even under Utility Quality Level D (QLD), the lowest level in the quality hierarchy, until reevaluated by a competent professional. For context, Utility Quality Level D is assigned to utility segments or features not visible at ground surface. The estimation of their positions is based on utility records, visual clues, or other second-party information reviewed and documented during a utility investigation. Record data is not automatically QLD, it must be evaluated in context with other pertinent information, including visual attributes, and then may be determined to achieve Quality Level “D”, based on the judgement of the professional overseeing the project.

Maintaining Data Integrity

This transition from CAD to GIS poses a significant challenge in maintaining the integrity and validity of utility data. The conversion process can involve alterations like shifting, rotation, or scaling, which may degrade the data's accuracy. Thus, once the data has been manipulated, it exits the realm of its certified format. It's essential to understand that the accuracy and precision of the data are valid only as of the time and in the medium it was certified and delivered. The data becomes stale at a point in time which may vary depending on the specific use of the data.

The Role of Professional Review in Reestablishing Data Quality

The data obtained from the GIS system can only be reassigned a quality level, such as QLD, after a thorough review by a professional and determination of the relationship to the project. This review process involves contextualizing the GIS data with other relevant project data and assessing its relevance and reliability. It's a critical step in ensuring that the utility data, now in a different format and potentially altered, still serves its intended purpose accurately and reliably.?

Conclusion

The conversion of CAD files to GIS within web GIS systems raises significant questions about data integrity and quality. It's crucial for professionals and users of this data to recognize that once SUE CAD data is converted to GIS, it loses its original quality certification. Any subsequent use of this data must involve a careful reassessment of its quality and applicability, ensuring that the integrity of utility records is maintained.

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