WGS 84 — three letters and two numbers that basically underpin every GPS fix you’ve ever gotten. I remember learning about it during my navigation training and thinking, “Okay, this is the kind of thing that sounds dry but is actually kind of wild once you dig in.” And it is. The fact that we’ve agreed on a single mathematical model of the Earth that everything from your phone to a Tomahawk missile references? That’s pretty remarkable.
So What Is WGS 84?
WGS 84 stands for World Geodetic System 1984. It was established by the US Department of Defense and it serves as the reference coordinate system for GPS, cartography, geodesy, and navigation. When your GPS says you’re at a certain latitude and longitude, those numbers are defined relative to WGS 84. Without it, your coordinates would be meaningless — or at least, they’d mean different things to different systems, which is arguably worse.
The system has three components: a standard coordinate frame for the Earth, a reference ellipsoid (basically a mathematical approximation of Earth’s shape), and a gravitational model for geodetic measurements.
The Coordinate System
WGS 84 uses a three-dimensional Cartesian coordinate system. Three axes — X, Y, and Z — all perpendicular to each other. The origin sits at Earth’s center of mass. The Z-axis points toward the North Pole. The X-axis points at where the Prime Meridian meets the Equator. And the Y-axis goes 90 degrees east of X, lying in the equatorial plane.
Probably should have led with this: every single GPS position you’ve ever used was calculated within this framework. It’s the invisible grid behind everything.
The Reference Ellipsoid
Earth isn’t a perfect sphere. It’s slightly squished at the poles and bulges a bit at the equator. The WGS 84 ellipsoid tries to capture that shape mathematically. It has an equatorial radius of 6,378.137 kilometers and a flattening constant of 1/298.257223563. These numbers enable consistent altitude calculations anywhere on the planet. Not perfect for every local spot, but remarkably good for a global model.
The Geoid
This is where it gets a little tricky. The geoid is a model of global mean sea level. It represents what the ocean surface would look like if it extended under the continents, influenced only by gravity. WGS 84 uses a specific geoid model to give more accurate surface elevation measurements. If you’ve ever wondered why your GPS altitude sometimes disagrees with the altimeter in your aircraft — the geoid is part of that story.
Practical Applications
In navigation, WGS 84 is the backbone. Every GPS satellite broadcasts its position in WGS 84 coordinates. Your receiver crunches those signals and gives you a position within the same system. Civilian users, military operators, maritime navigators — everyone’s on the same page.
Cartographers use WGS 84 to produce maps with a standardized reference frame. That matters more than you’d think. Before global standards, maps from different countries could disagree on the position of the same mountain by hundreds of meters. That’s what makes WGS 84 endearing to mapmakers — it ended a lot of those arguments.
Geodesy, the science of measuring Earth’s shape and gravitational field, leans on WGS 84 for consistent measurements. Scientists monitoring tectonic movement, sea level changes, or ice sheet dynamics all reference this system.
How It Relates to Other Systems
WGS 84 is closely aligned with the International Terrestrial Reference Frame (ITRF). Over the years, the system has been refined to stay compatible with the latest ITRF coordinates. Earlier versions of WGS existed too, but 84 is the one that stuck because it was designed with satellite technology in mind from the start.
Updates and Revisions
WGS 84 hasn’t stayed frozen since 1984. There have been several refinements. The G730 revision in 1994, then G873, then G1150 — each one incorporated better gravitational field measurements and improved satellite tracking data. The system keeps getting more precise, which is exactly what you want from a global reference frame.
Ellipsoid Parameters (For the Numbers People)
- Equatorial radius (semi-major axis): 6,378,137 meters
- Polar radius (semi-minor axis): 6,356,752.3142 meters
- Flattening: 1/298.257223563
- First eccentricity squared: 0.00669437999014
- Second eccentricity squared: 0.00673949674227
The Geodetic Datum
WGS 84 functions as both a coordinate frame and a datum. The datum provides the framework that GPS measurements reference. It’s defined and maintained by the National Geospatial-Intelligence Agency (NGA), which probably tells you something about how seriously the US government takes positional accuracy.
Strengths and Limitations
The big advantage of WGS 84 is its global applicability. One system, everywhere, for everyone. But no global model is perfect for every local area. Some regions have localized geodetic systems that fit better for their specific geography. If you’re surveying a small plot of land in, say, rural Norway, a local datum might give you slightly better accuracy than WGS 84. For everything else — air navigation, maritime operations, global mapping — WGS 84 is the standard.
WGS 84 in Modern Technology
It’s everywhere. Autonomous vehicles use it. Your smartphone uses it. Every navigation app, every drone controller, every precision agriculture system. The consistency and reliability of WGS 84 is what makes real-time location services possible at a global scale.
Satellite technology and geodetic measurements continue to improve, and WGS 84 evolves with them. It’s the foundation of global navigation and it’s not going anywhere — which, for a system designed in the early 1980s, is a pretty impressive legacy.
