Mount Everest, with an elevation of 8,848 metres, is Earth’s highest mountain above sea level.

Ever taken a picture from the top of a mountain and wondered what number to put in the caption to tell the world how high you are? The number you are looking for is called elevation.

What is elevation?

Simply put, elevation is a geographical term used to describe the vertical distance between a predetermined reference point (such as mean sea level) and the top of an object (such as a mountain). Commonly confused with altitude, the basic difference between the two is that elevation refers to the height of a point on the Earth’s surface measured from a fixed reference datum, whereas altitude is used to measure the height of a point above the Earth’s surface — for example, the cruising height of an aircraft.

How is elevation calculated?

In 2015, North America’s tallest mountain, Mount McKinley, was officially renamed Denali. Alongside that change, the US Geological Survey announced a revised summit elevation of 20,310 feet (6,190 metres), shaving 10 feet off the previously accepted figure of 20,320 feet (6,194 metres).

GPS equipment being set up at Denali’s highest point for precise summit elevation data. Credit: Blaine Horner / CompassData

Historically, elevation was calculated using trigonometry. By measuring the horizontal distance between two points and the vertical angle between them, surveyors could determine the relative elevation of an object. Denali’s earlier elevation was determined using aerial radar measurements, but even that technique proved insufficiently precise.

Today, modern GPS techniques are used to determine the elevation of a location. A GPS receiver needs signals from at least four satellites to compute a three-dimensional position fix — latitude, longitude, and height — above a reference ellipsoid.

In practice, this is more complex than it sounds. GPS receivers can return different elevation values depending on the vertical datum they reference. Because the Earth’s surface is not a perfect sphere or ellipsoid, scientists have developed various theoretical models called vertical datums to represent the shape of the planet and provide a consistent baseline for elevation measurements.

How can I find my elevation?

By now, you may be curious to find the elevation of your current location. Fortunately, you do not need to master the mathematics of geodesy to satisfy that curiosity. There are a number of web tools available for exactly that purpose. Elevation Map, for example, uses data from LiDAR digital elevation models to give you an approximate elevation value for any location with a simple click.

For more professional use, Google Maps Platform offers an Elevation API as part of its Maps JavaScript API. This API provides elevation data for any location on the Earth’s surface and also returns negative values for depth locations on the ocean floor.

To summarise: elevation is the vertical distance between a point on the Earth’s surface and a reference datum, most commonly mean sea level. Various vertical datums govern how elevation is measured, and understanding them is important for using elevation data effectively.