A vertical datum provides a consistent reference surface for measuring elevations. The North American Vertical Datum of 1988 (NAVD88) is the standard for elevation measurements across the United States, Canada, and Mexico, ensuring data consistency across locations and times.
Understanding NAVD88
NAVD88 is a fixed reference surface used to precisely measure heights across the North American continent. The datum was established through a network of geodetic leveling surveys, creating a comprehensive system for vertical control. Its foundation is rooted in a single origin point at Father Point (Pointe-au-Père) in Rimouski, Quebec, Canada.
This datum was affirmed as the official vertical datum for the United States in the National Spatial Reference System (NSRS) in 1993. NAVD88 improved upon its predecessor, the National Geodetic Vertical Datum of 1929 (NGVD29), by incorporating adjustments for observed gravity and relying on a more extensive network of leveled land and benchmarks. NGVD29 was based on observations from 26 tide stations, which introduced inaccuracies due to variations in sea surface topography. NAVD88, by contrast, simplified its origin to a single, continuously monitored tide station, leading to more consistent observations.
Why NAVD88 Matters
NAVD88 is applied across many sectors. It is fundamental for surveying, mapping, engineering, and construction projects, ensuring structures and infrastructure are built to correct relative elevations. Beyond construction, NAVD88 plays a role in environmental planning, such as managing floodplains and studying sea-level rise. This consistent reference allows professionals to accurately compare measurements taken by different individuals or agencies, leading to safer and more effective outcomes.
Without a unified vertical datum, elevation data would be inconsistent, leading to problems. For instance, inaccurate elevation data can result in misaligned construction, incorrect flood plain delineations, and increased project costs. A slight difference in elevation reference could cause buildings to not align properly or lead to inaccurate flood insurance rates for properties. Accurate elevation comparison is important for effective water flow management and for ensuring that various geospatial products align correctly.
How NAVD88 is Determined and Applied
The establishment and application of NAVD88 rely on a network of physical markers known as benchmarks, each with a precisely determined NAVD88 elevation. These benchmarks serve as fixed reference points for surveyors and engineers. Traditional leveling surveys, involving precise measurements of elevation differences, were instrumental in determining initial NAVD88 elevations.
Modern techniques complement these traditional methods, with Global Positioning System (GPS) and Global Navigation Satellite System (GNSS) technologies used in conjunction with geoid models to derive NAVD88 elevations. The National Geodetic Survey (NGS), an agency within the National Oceanic and Atmospheric Administration (NOAA), is responsible for maintaining and providing access to NAVD88 data. Professionals use these benchmarks and data provided by NGS to ensure their projects adhere to the correct elevation standards, enabling seamless integration of data across various applications.
Looking Beyond NAVD88
Despite its widespread use, NAVD88 has limitations that prompted the development of a new vertical datum. Its reliance on a single tide gauge and susceptibility to crustal movement present challenges for modern, precise positioning technologies. NAVD88 also does not fully integrate with current satellite-based positioning systems like GPS and GNSS, which are now standard tools for geospatial measurements.
To address these limitations, the National Geodetic Survey is preparing to implement a new vertical datum, the North American-Pacific Geopotential Datum of 2022 (NAPGD2022). This new datum is designed to be more accurate and compatible with modern satellite measurements, as it will be based on gravity and satellite data rather than traditional leveling networks. While the full implementation of NAPGD2022 was initially planned for 2022, it has been delayed and is now anticipated for 2025 or 2026. Until then, NAVD88 remains the official and widely used vertical datum.