Yes, the U.S. survey foot is officially obsolete for general use as of January 1, 2023. At the stroke of midnight on New Year's Day, 2023, this measurement unit was formally retired, with the international foot now serving as the standard for all new measurements in the United States.
The Official Retirement of the U.S. Survey Foot
The decision to deem the U.S. survey foot obsolete was made to simplify and unify measurement standards across the globe and within the United States. For decades, two slightly different definitions of the "foot" coexisted in the U.S.: the international foot and the U.S. survey foot. This duality could lead to confusion and errors, particularly in large-scale precise mapping and surveying projects.
The international foot is defined as exactly 0.3048 meters. This definition has been uniformly adopted by the National Institute of Standards and Technology (NIST) and the National Geodetic Survey (NGS) for all new surveying and mapping applications. This change ensures consistency with international measurement standards.
While the U.S. survey foot is now retired from active use for new data, it remains relevant for historical and legacy applications. Existing data, maps, and surveys that were based on the U.S. survey foot definition do not instantly become invalid but require careful handling and conversion when integrated with new international foot-based data.
Understanding the Difference
The distinction between the U.S. survey foot and the international foot is extremely small but significant for high-precision work over long distances.
| Feature | U.S. Survey Foot | International Foot |
|---|---|---|
| Definition | 1200/3937 meters (approximately 0.3048006096 meters) | Exactly 0.3048 meters |
| Primary Use | Historically used in U.S. surveying and mapping | Standard global and current U.S. measurement |
| Status | Obsolete for new measurements since Jan 1, 2023 | Standard for all new measurements |
| Difference | Approximately 2 parts per million longer than the international foot | The established precise standard |
This subtle difference means that over a mile, the U.S. survey foot is about 3.2 millimeters longer than the international foot. Over larger distances, such as 100 miles, this discrepancy accumulates to approximately one foot.
Implications for Surveying, Mapping, and GIS
The transition has several key implications for professionals in surveying, mapping, geographic information systems (GIS), and engineering:
- Data Compatibility: All new spatial data should now exclusively use the international foot. When integrating legacy data with new data, careful conversion is essential to prevent cumulative errors.
- State Plane Coordinate Systems (SPCS): Many U.S. State Plane Coordinate Systems were historically defined using the U.S. survey foot. States were given a transition period to decide how to manage this change within their geodetic frameworks. Users should consult state-specific guidelines.
- Software Updates: Most modern surveying and GIS software packages have been updated to reflect this change, allowing users to specify the foot definition or handle conversions automatically. However, verifying the chosen standard is crucial.
- Legal and Contractual Clarity: Professionals must clearly specify which "foot" unit is being used in contracts, reports, and legal documents to avoid ambiguity and potential disputes, especially when referencing older property descriptions.
Practical Insights
To navigate this transition effectively:
- Always use the international foot for all new projects, measurements, and data creation. This ensures compliance with current standards and international compatibility.
- Identify the measurement standard of existing datasets. Older data may implicitly or explicitly use the U.S. survey foot. It's critical to know the source unit before using or combining data.
- Perform accurate conversions when mixing old and new data. Conversion tools and formulas are widely available, or can be managed by updated software.
- Stay informed by regularly checking updates from authoritative bodies like the National Institute of Standards and Technology (NIST) regarding measurement standards. More information on this transition can be found on the NIST website.
- Consult state and local geodetic agencies for specific guidance on how this change impacts regional or local coordinate systems and regulations.
While the U.S. survey foot is no longer the standard for new work, its historical presence means that awareness and careful handling are still necessary for dealing with legacy information and ensuring accuracy in all spatial applications.
