Elevation in geography defines the vertical distance of a point on the Earth’s surface relative to a consistent, established starting point. This measurement describes the topography, or shape, of the land, including mountain peaks, valley floors, or features below the water surface. Elevation provides a fundamental value for understanding the physical landscape.
The Fixed Reference Point
To establish a standard measurement for elevation, a fixed zero point is necessary, which is known as a vertical datum. The most commonly used reference surface is Mean Sea Level (MSL), which represents the average height of the ocean’s surface over a long period. This averaged surface is modeled by the geoid, an equipotential surface that closely approximates MSL and extends under the landmasses.
Elevation values are determined as being either above or below this established geodetic datum. For example, a mountain peak has a positive elevation, while a point in a deep ocean trench has a negative value. Since MSL varies globally due to factors like gravity, specific national or regional datums, such as the North American Vertical Datum of 1988 (NAVD 88), are used to provide a consistent reference for local surveying and mapping.
Elevation, Altitude, and Height: Understanding the Differences
Although often confused, elevation, altitude, and height each describe a distinct vertical measurement. Elevation is the vertical distance of a point on the Earth’s surface relative to the established vertical datum (MSL). It describes how high the land itself is, such as the elevation of a city or the top of a hill.
Altitude refers to the vertical distance of an object above a reference level, which may be MSL or the ground surface. This term is most frequently used in aviation to describe how high an aircraft is flying. For instance, a plane flying over a mountain has an altitude, while the mountain itself has an elevation.
Height is the most general term, describing the vertical distance of an object above its immediate base. This measurement is used for structures or features that rise from the ground, such as a skyscraper or a tree. A building’s height is measured from its foundation to its roof, while its elevation is measured from the foundation’s location to the geodetic datum.
How Elevation is Measured and Represented
The determination of precise elevation values relies on various practical measurement techniques. Traditional methods involve ground surveying, which uses instruments like leveling tools to measure differences in height between a known benchmark and the target point. Modern technology offers greater efficiency and accuracy through the use of Global Navigation Satellite Systems (GNSS), such as GPS, which calculate vertical position relative to a geometric model of the Earth.
Remote sensing technologies, including Light Detection and Ranging (LiDAR), are employed to map large areas by emitting laser pulses and measuring the time it takes for the light to return. This dense collection of data points is used to create Digital Elevation Models (DEMs), which are computer-generated representations of the terrain. On physical maps, elevation data is visually represented by contour lines, which are continuous lines that connect all points of equal elevation.
The spacing between these contour lines indicates the steepness of the terrain, with closely spaced lines representing a steep slope and widely spaced lines indicating a gentler gradient. Contour maps, also known as topographic maps, may also use color gradients or shading to visually enhance the sense of relief.