geoid
Sea-level reference surface
A geoid is the shape the Earth would have if its surface were entirely covered by ocean at rest—a lumpy sphere determined by gravity rather than topography.
Geodesists use this theoretical surface as a reference for measuring elevation, since the actual Earth bulges and dips according to variations in mass distribution beneath the surface.
Single unit of information
- benchmarkStandard for comparison
- levelingMaking flat or equal
- triangulationLocation via three points
- surveyingMeasuring and charting terrain
coordinates · adjustment · network · baseline · theodolite · plumbline · altimetry · reference frame
Nearly round solid
- oblateSquashed-sphere shape
- ellipsoidOval solid shape
- equipotentialHaving uniform potential throughout
- undulationRhythmic rise and fall
bulge · flattening · irregularity · deviation · approximation · curvature · polar · equatorial
Having uniform potential throughout
- gravitationMutual pull between masses
- accelerationRate velocity changes
- mean sea levelAverage ocean surface height
- gravimetryMeasuring gravitational field strength
gravimeter · anomaly · deflection · plumbline · vertical · attraction · mass distribution · density
Average ocean surface height
- ocean surfaceTop of the sea
- continentalOf a continent
- terrainLand's physical features
- topographyPhysical feature mapping
hydrosphere · lithosphere · geophysics · global · planetary · geomorphology · bathymetry · elevation
Satellite-based location technology
- gravimetryMeasuring gravitational field strength
- levelingMaking flat or equal
datum
Single unit of information
- benchmarkStandard for comparison
- levelingMaking flat or equal
- triangulationLocation via three points
surveying · coordinates · adjustment · network · baseline · theodolite · plumbline · altimetry · reference frame · control point
spheroid
Nearly round solid
- oblateSquashed-sphere shape
- ellipsoidOval solid shape
- equipotentialHaving uniform potential throughout
undulation · bulge · flattening · irregularity · deviation · approximation · curvature · polar · equatorial · surface
equipotential
Having uniform potential throughout
- gravitationMutual pull between masses
- accelerationRate velocity changes
- mean sea levelAverage ocean surface height
gravimetry · gravimeter · anomaly · deflection · plumbline · vertical · attraction · mass distribution · density · isostasy
mean sea level
Average ocean surface height
- ocean surfaceTop of the sea
- continentalOf a continent
- terrainLand's physical features
topography · hydrosphere · lithosphere · geophysics · global · planetary · geomorphology · bathymetry · elevation · relief
GPS
Satellite-based location technology
- gravimetryMeasuring gravitational field strength
- levelingMaking flat or equal
- Euclidean geometryStudy of flat planes
- local geographyPhysical features of an area
- geologic historyEarth's temporal record
- geologic erasMajor divisions of deep time
- world geographyStudy of Earth's places
- US geographyPhysical features of America
geography, geometry, geology, geographer, geologic, geodesy, geo, geochemistry, geomagnetic