- In surveying and geodesy, a
**datum**is a reference system or an approximation of the Earth's surface against which positional measurements are made for computing locations.**Horizontal****datums**are used for describing a point on the Earth 's surface, in latitude and longitude or another coordinate system.

en.wikipedia.org/wiki/Geodetic_**datum**- In surveying and geodesy, a

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**horizontal datum**is a specified coordinate system for a collection of positions on the surface of the earth. Traditionally,**horizontal****datums**have used classical surveying methods (i.e. Measuring distances and angles through triangulation surveys) to best fit to the surface of the earth. A geometric**datum**is a coordinate system for collection ...A

**horizontal datum**provides a reference frame for coordinates on Earth. A long time ago, surveyors put brass monuments in the Earth with precise X, Y locations. When these monuments were combined together using a technique called triangulation, this formed our**horizontal datum**.- youtube.com
**Horizontal**/Geometric Datums by Dave Doyle - youtube.com
**Horizontal**Datums/Levels in SUBstructure - youtube.com
**Horizontal**Datums in SUPERstructure - youtube.com
**Horizontal**and vertical**datum**in surveying

**Horizontal datums**are used for describing a point on the Earth's surface, in latitude and longitude or another coordinate system. Vertical**datums**are used to measure elevations or underwater depths.**Horizontal datum**. The**horizontal datum**is the model used to measure positions on the Earth.**Horizontal datums define**the geometric relationship between a coordinate system grid and the Earth's surface. Because the Earth's shape is complex, the relationship is too. The goal of this section is to explain the relationship.At its most basic level of definition, the

**horizontal datum**is a collection of specific points on the Earth that have been identified according to their precise northerly or southerly location (latitude) and easterly or westerly location (longitude).The

**horizontal datum**is the one that is used in measuring a specific position on the earth's surface in coordinate systems such as latitude and longitude.- Amanda Briney

Jul 12, 2018 · The North American Datum of 1927 (NAD 27) is "The

**horizontal**control datum for the United States that (was) defined by (a) location and azimuth on the Clarke spheroid of 1866, with origin at (the survey station) Meades Ranch." ... The geoidal height at Meades Ranch (was) assumed to be zero.The term

**horizontal datum**is used because it is more easily flattened into 2 dimensions and more useful for finding locations on a flat plane (compared to a**vertical datum**). As in the ESRI post you referenced (image below), the Earth's surface is very uneven, so modeling this very difficult.A

**horizontal datum**provides a frame of reference as a basis for placing specific locations at specific points on the spheroid. Geodesists use a**horizontal datum**as the model to translate a spheroid / ellipsoid into locations on Earth with latitude and longitude lines. Geodetic**datums**form the basis of coordinates of all**horizontal**positions on Earth.NAD 23 CONUS

**datum**is one of these terrestrial based**datums**established from a triangulation station in Meades Ranch, Kansas. As space based surveying came into use, a standardized**datum**based on the center of the earth and an ellipsoid the was a good fit to the entire surface of the earth was developed.