(n) A theoretically exact point, axis, or plane used as a reference for tabular dimensioning. A datum marks the origin from which the location and orientation of geometric features are established.

A set of parameters specifying the reference surface or the reference coordinate system used for geodetic control in the calculation of coordinates of the points of the earth. Commonly, datums are defined as horizontal and vertical datums separately. For the practical use of datum it is necessary to have one or more well monumented points with coordinates given in that datum.

A reference point from which movements or measurements are made. A datum can lie anywhere on the surface of a work piece. A datum can be a coordinate but does not have to have a physical feature.

Properly, is the singular for the word data. In mapping, it is the assumed horizontal surface of zero elevation. This surface forms a spheroid (defined mathematically) and is meant to approximate the shape of the earth. Survey control positions are relative to a given datum. See NAD27, NAD83.

a fixed or established point of reference, usually with a fixed elevation

a fixed reference point on an archaeological site from which measurements are taken.

Standard or common reference base or system.

Something used as the basis for reasoning, inference, calculating, or measuring. A reference point or origin for mapping.

(pl. datums) A point, line, or surface used as a reference, as in surveying or mapping.

The units of latitude and longitude, each datum describes the shape of the Earth differently. Most GPS units use the datum WGS-84, while older maps in the US use NAD27.

(1) In general terms, a single isolated piece of information. (2) A fixed reference point or basis to which other information is related. (3) A set of accurately surveyed horizontal control points that define the shape of the Earth as a spheroid and form the basis for a 2-dimensional coordinate system. (4) A vertical datum is a level surface of reference (usually mean sea level or the geoid) from which elevations are measured. (See -North American Datum 1983 (NAD 83) and Spheroid).

The point from which measurements are taken.

(pl. datums) A model of the earth's surface that is comprised of a network of physical points that serves as a reference for maps, for both horizontal and vertical data. In the U.S. early topographic maps were based on the North American Datum 1927 (NAD27). More recent maps are based on a North American Datum 1983 (NAD83). GPS uses a datum called World Geodetic System 1984 (WGS84). There are over 100 datums in use around the world.

All ground surface elevations are measured from a certain point called a datum. Once TSARP is completed all of the elevation data for Harris County will be on NAVD 1988 2001 Adjustment Datum. Back

Based upon a spheroid, a datum acts a starting point for making the most accurate measurements on Earth's surface. A datum is a local point of reference, and as such there is a different datum for almost every region of the planet.

A reference point of starting elevations used in mapping and surveying.

A base or reference elevation used as the origin to define subsequent elevation. Often refers to mean sea level.

A reference location or elevation which is used as a starting point for subsequent measurements. Sea level is a datum for elevation measurements. Datums can also be arbitrary such as the starting point for stream stage measurements or based upon a physical feature such as the base of a rock unit.

A value that serves as a reference for measuring other values of the same quantity.

is an elevation above mean sea level to which all gage height readings are referenced.

A datum is a network of monuments and reference points defining a mathematical surface from which geographic computations can be made. [Section 4.3.1.1

a "base value" or "reference value" from which other values can be calculated

a feature or group of features of a part selected for use as a base from which other features or points are located within specified limits

a fixed point that anchors a sketch point to a specified location

a fixed, three-dimensional surface, an oblate spheroid, that is approximately the size and shape of the Earth

a form which ascribes data mathematically along a grid standard for map production

a frame of reference when plotting locations on a globe

a framework that enables us to define coordinate systems

a geodetic reference system that specifies the size and shape of the earth, and the base point from which the latitude and longitude of all other points on the earth's surface are referenced

a known or assumed point used as a basis for inference or reckoning

a location-specific reference surface to which all measurements are reduced for locational referencing

a mathematical figure that best fits the shape of the Earth

a mathematically defined reference surface which approximates the shape of the earth, and enables calculations such as position and area to be carried out in a consistent and accurate manner

a mathematical model of the earth used to calculate the coordinates on a map, chart, or survey system

a mathematical model of the Earth which approximates the shape of the Earth, and enables calculations such as position and area to be carried out in a consistent and accurate manner

a mathematical model of the world's shape, and is used to calculate the coordinates on any map or chart

a mathematical model that describes the size and shape of the Earth (an ellipsoid) and provides the origin and orientation of the coordinate system

a mathematical model that represents the shape of the earth

a mathematical representation of the earth

a mathematical surface on which a mapping and co-ordinate system is based

a means by which coordinates determined by any means may be related to a well-defined Reference Frame

a model of the surface of the earth based on a surveyed network of physical points

an attempt by map makers to correct for the fact that the earth isn't perfectly round, but rather elliptical in shape

a plane that extends off to infinity

a point, a line, or surface used as a reference in surveying and mapping

a point of known location or elevation, from which other locations or elevations can be measured

a point on the earth's surface that is used to anchor a map

a reference for physical parameters such as the shape of the earth

a reference point of known or assumed height to which all other site levels will refer

a regional or global coordinate reference system

a set of constants or control points that specify the coordinate system used for geodetic control, i

a set of control points whose geometric relationships are known, either through measurement or calculation, and is used to define a coordinate system

a set of parameters defining a coordinate system, and a set of control points whose geometric relationships are known, either through measurement or calculation

a set of parameters which define the coordinate system of a projection

a smoothed mathematical surface of the earth's mean, sea- level surface

a specialized coordinate reference concept that also includes an Ellipsoid - a definition of the exact non-sphericity of the planet

a standard representation of shape and offset for coordinates, which includes an ellipsoid and an origin

a surveyed line or point that ensures all maps within a series will correctly match when placed edge to edge

a surveying or referencing system used as a basis for calculating and/or measuring geographic locations

Any point, line or surface used as a reference for a measurement of another quantity. A model of the earth used for Geodetic calculations. A more complete explanation is available in the Standards Section.

A network of precisely-surveyed control points used as a reference for measurements of other horizontal or vertical positions. For global-scale measurements, the WGS 84 ellipsoid also serves as a datum. Reference: Peter Dana, The Geographer's Craft

a mathematical reference framework for geodetic coordinates defined by the latitude and longitude of an initial point, the azimuth of a line from this point, and the parameters of the ellipsoid upon which the initial point is located. In regard to usage in this catalog, datum is identifying which system the coordinates are based upon (NAD27 or NAD83)

A position or element in relation to which others are determined. Datum Line: A line from which distances or dimensions are reckoned. Datum Plane: A plane from which distances or dimensions are reckoned. Datum point: A point used as the basis for reckoning.

A datum is something used as a basis for calculating and measuring. In the case of GPS, datums are different calculations for determining longitude and latitude for a given location. Currently, Geocaching uses the WGS84 datum for all caches. Many maps still use NAD27, which can cause confusion if your GPS unit is set to NAD27. Always check your GPS to ensure that WGS84 is the datum before entering a cache coordinate into your unit.

a point, line, surface or set of quantities used as a reference upon which measurements are based

A reference surface for a particular coordinate system. Defines the mathematical relationship by which a feature relates to its original surface in a specific coordinate system.

(pl. datums) a reference system for surveying which involves using a plane, level, line, etc., from which to calculate heights and depths. A vertical datum is a level surface to which heights are referred. The horizontal datum is used as a reference for position. Position coordinates are assigned to actual locations based on an underlying ellipsoidal model of the earth used for drawing the map. Typical USA Datums are WGS84 and NAD27.

A Datum is a framework that defines a coordinate system and includes the parameters defining the earthâ€™s surface.

An arbitrary Elevation from which all vertical measurements are taken in a design

Technically, the point from which co-ordinates on a map begin, but the term can also refer to the entire co-ordinate system. There are two map datums commonly used in Australia: the Australian Geodetic Datum 1966 ( AGD66), which is found on older maps, and the newer Geocentric Datum of Australia 1994 ( GDA94) which has superceded it

In surveying, a reference system for computing or correlating the results of surveys. There are tow principal types of datums: vertical and horizontal. A vertical datum is a level surface to which heights are referred. In the United States, the generally adopted vertical datum for leveling operations is the National Geodetic Vertical Datum of 1929. The horizontal datum is used as a reference for position. The North American Datum of 1927 is defined by the latitude and longitude of an initial point (Meade's Ranch in Kansas), the direction of a line between this point and a specified second point, and two dimensions that define the spheroid. The new North American Datum of 1983 is based on a newly defined spheroid (GRS80); it is an Earth-centered datum having no initial point or initial direction.

an assumed horizontal reference plane used as a basis for computing elevations

Geographical reference frame, horizontal plane based on a vertical benchmark (such as mean sea level)

The basis for relating river stage to mean sea level. (datum + stage = elevation in feet above mean sea level)

A theoretically exact plane, point or axis from which a dimensional measurement is made.

A reference line or point from which measurements are taken.

A geographic model obtained by referencing the earth's sea level surface area and applying theoretical mathematical calculations. Map datums may vary from chart to chart. The map datum for your GPS unit should match the datum listed on the corresponding chart. Refer to the map legend to find the specific datum for your chart.

A reference plane, point or diameter that provides a base for calculations and measurements.

In mapping, a numeric or geometric quantity which serves as a reference or base to accurately define other quantities. It most often refers to either a horizontal standard, such as a particular spheroid for referencing coordinate positions, or it refers to a vertical datum, such as mean sea level, from which elevations are referenced.

Any level surface taken as a plane of reference from which to measure elevations.

A math model which depicts a part of the surface of the earth. Latitude and longitude lines on a paper map are referenced to a specific map datum. The map datum selected on a GPS receiver needs to match the datum listed on the corresponding paper map in order for position readings to match. DCG® See Depth Controlled Gain.

(n.) a single quantity that may have any of the set of values specified in its data type.

1. Any numerical or geometrical quantity or set of such quantities which may serve as a reference or base for other quantities. See chart datum

Map Datum's are the reference system used between the Lat/Longs and the map being used as a reference. There are hundreds of them, and you have to tell your GPS unit which one to use. This site, Garmin and Delorme default to WGS84.

An Earth-shape (ellipsoid) reference model upon which points on the Earth's surface are calculated. For instance, NAD27 is common for UTM 1:24000 DRGs and 30m and 10m DEMs, though corresponding DOQs may be in a different datum, such as NAD83. Draping data from one datum, such as images or DLGs, onto DEMs in another datum, will result in noticeable misalignments.

A reference, such as a line, or plane, in relation to which the position of other elements is determined.

Set of parameters and control points used to accurately define the three-dimensional shape of the earth. The corresponding datum is the basis for a planar coordinate system.

Any position or element in relation to which others are determined, as datum point, datum line, DATUM PLANE. See Figure 11.

a point, line, plane, cylinder, axis, etc., from which the location or geometric relationship of other part features may be established or related

A fixed reference point from which levels are set out.

The theoretical exact point, axis, or plane from which the location of geometric characteristics or features of a part are dimensionally established. Whence datum intersection (origin) The point of intersection of the X and Y datums on a circuit board and the origin (0,0 point) of the layout grid. The 0, 0 point of a layout grid, usually located in the lower left corner of a board.

A geodetic coordinate system which is specific to a given geographical region.

A reference system for vertical and horizontal positions. Different datums have different positions for the physical location of their origins, thus different datums will represent coordinates in different positions. Differences can be as much as a mile. All reliable maps that show coordinate systems provide Datum information.

A point from which other things are measured. This term (in full, geodetic datum or geocentric datum) can also refer to a cartographical system (specifically, a reference ellipsoid, such as WGS84) that is used to mathematically correct for irregularities in the Earth's sphericity, such as when using the GPS.

The level from which altitudes are measured. Generally mean sea level.

A base elevation used as a reference from which to reckon heights or depths. In order that they may be recovered when needed, such datums are referenced to fixed points known as bench marks. See chart datum.

A benchmark in surveying which is a point of known location ( in 3D space and in relation to sea level). Datum is also a word used in archaeology to represent an individual measurement, the sum of individual datum is data.

A fact either indubitably known or treated as such for the purpose of a particular discussion. A known reference. A point, line, or plane used as a basis for referring measurements.

a mathematical approximation to all or part of the earth's surface. Defining a datum requires the definition of an ellipsoid, its location and orientation, as well as the area for which the datum is valid.

A reference point from which other points in a survey are measured from. A datum may be a known point within an existing survey grid or it may be any arbitrary point. For a more detailed explanation of datums revise A Coordinate Datum.

A datum is used as a basis for calculating and measuring. In the case of GPS, datums are different calculations for determining longitude and latitude for a given location. Always check your GPS to ensure that WGS84 is the datum before entering a cache coordinate into your unit. Lots of maps still use NAD27 and the datum must be converted as geocaching currently uses WGS84.

A basis or measurement foundation on which a location can be defined or referenced either vertically, horizontally or both.

A math model designed to fit part of the earth's surface. Latitude and longitude lines on a paper map are referenced to a specific map datum. The map datum for a GPS receiver needs to match the datum listed on the corresponding paper map.

A horizontal plane elevation used as a reference plane.

Changing technology has led to different values for the same geographic points over time. Datum refers to which standard you are using for known points. If you are going to use your collected data with prexisting data, you need to match up the datum and coordinate systems. Some examples of datum are NAD-27 and WGS-84 (North American Datum 1927, World Geodetic System 1984).

Any numerical or geometrical value, surface, line, or point which may serve as a base or reference for other quantities.

1. The fixed starting point for surveying or measuring. 2. A piece of information.

The vertical or horizontal reference system associated with particular coordinates and elevations. Consists of a model of the earth (ellipsoid) and a physical location chooses as the origin point. Latitude and longitude lines are referenced to a specific map datum. The GPS receiver map datum must match the datum on the corresponding paper maps in order for position readings to match.

a single fact, as in: We based our measurements on the datum of the boiling point of water. (Note: rarely used outside scientific literature)

Any level taken as a reference level.

A horizontal plane from which heights and depths are measured.

A base reference level for the third dimension of elevation for the earth’s surface. A datum can depend on the ellipsoid, the earth model, and the definition of sea level.

For marine applications, a base elevation used as a reference from which to reckon heights or depths. It is called a tidal datum when defined in terms of a certain phase of the tide. Tidal datums are local datums, referenced to fixed points (bench marks), and should not be extended into areas that have differing hydrographic characteristics without substantiating measurements.

Theoretically exact planes, lines or points from which other features are located on design drawings.