Georeferencing Calculator Manual

Button used to calculate coordinates and uncertainty using the point-radius method (Wieczorek et al. 2004), based on the values of parameters pertinent to the selected Locality Type. Clicking on the Calculate button fills in the results section of the Calculator formatted as Darwin Core fields that need to be recorded for a georeference that follows the Georeferencing Best Practices (Chapman & Wieczorek 2020) (i.e. decimalLatitude, decimalLongitude, geodeticDatum, coordinateUncertaintyInMeters, coordinatePrecision, georeferencedBy, georeferencedDate, and georeferenceProtocol). The calculation combines the sources of uncertainty using an algorithm appropriate to the locality type (see Calculating Uncertainties in Georeferencing Best Practices). The calculations account for uncertainties due to coordinate precision, unknown datum, data source, GPS error, measurement error, feature geographic radial, distance precision, and heading precision.

Defines the original geographic coordinate format (decimal degrees, degrees minutes seconds, degrees decimal minutes) of the coordinate source. Equivalent to the Darwin Core term verbatimCoordinateSystem. Selecting the original Coordinate Format allows the coordinates to be entered in their native format and forces the Calculator to present appropriate options for Coordinate Precision. Note that changing the Coordinate Format will reset the Coordinate Precision value to "nearest degree". Be sure to correct this for the actual coordinate precision. Behind the scenes, the Calculator stores coordinates in decimal degrees to seven decimal places. This is to preserve the correct coordinates in all formats regardless of how many transformations are done.

Labelled as Precision in the first column of input parameters, this drop-down list is populated with levels of precision in keeping with the Coordinate Format chosen for the verbatim original coordinates. This is similar to, but NOT the same as the Darwin Core term coordinatePrecision, which applies to the output coordinates. A value of "exact" is any level of precision higher than the otherwise highest precision given on the list.

Labelled as Precision in the results, this text box is populated with precision of the output coordinates, and as such is equivalent to the Darwin Core term coordinatePrecision. The precision of the output in the Calculator is always "0.0000001", no matter how many digits appear to the right of the decimal indicator in the Output Latitude and Output Longitude.

The resources (map, GPS, gazetteer, locality description) from which the Input Latitude and Input Longitude were derived. Related to, but NOT the same as the Darwin Core term georeferenceSources, which requires the specific resources used rather than their characteristics. Note that the uncertainties from the two sources "gazetteer" and "locality description" can not be anticipated universally, and therefore do not contribute to the uncertainty in the calculations. If the error characteristics of the specific sources of this type are known, they can be added in the Measurement Error before calculating. If the source "GPS" is selected, the label for Measurement Error will change to GPS Accuracy, which is where accuracy distance of the GPS at the time the coordinates were taken should be entered. For details on GPS Accuracy see Using a GPS in Georeferencing Best Practices (Chapman & Wieczorek 2020).

Defines the position of the origin and orientation of an ellipsoid upon which the coordinates are based for the given Coordinate Source. Equivalent to the Darwin Core term geodeticDatum. The Calculator includes ellipsoids on the Datum drop-down list, as sometimes that is all that coordinate source shows. The choice of Datum has two important effects. The first is the contribution to uncertainty if the datum of the source coordinates is not known. If the datum and ellipsoid are not known, choose the option "datum not recorded". Uncertainty due to an unknown datum can be severe and varies geographically in a complex way, with a worst-case contribution of 5359 m (see Coordinate Reference System in Georeferencing Best Practices (Chapman & Wieczorek 2020). The second important effect of the Datum selection is to provide the characteristics of the ellipsoid model of the earth, which the distance calculations depend on.

The heading given in the locality description, either as a standard compass point (see Boxing the compass) or as a number of degrees in the clockwise direction from north. If "degrees from N" is selected, there will appear a text box to the right of it in which to enter the degree heading.

Labelled as Precision in the second column of input parameters. Refers to the precision with which a distance was described in a locality (see Uncertainty Related to Offset Precision in Georeferencing Best Practices (Chapman & Wieczorek 2020). This drop-down list is populated in keeping with the Distance Units chosen and contains powers of ten and simple fractions to indicate the precision demonstrated in the verbatim original offset.

Denotes the real world units used in the locality description. It is important to select the original units as given in the description, because this is needed to properly incorporate the uncertainty from distance precision.

Button used to copy and potentially convert the calculated coordinates from the Output Latitude and Output Longitude into the Input Latitude and Input Longitude fields in preparation for a new calculation based on the previous results, eliminating the need to copy manually or to use cut and paste keyboard combinations.

When "GPS" is selected from the Coordinate Source drop-down list, the label for the Measurement Error text box changes to GPS Accuracy. Enter the value given by the GPS at the time the coordinates were captured. If not known, enter 100 m for standard hand-held GPS coordinates taken before 1 May 2000 when Selective Availability was discontinued. After that, use 30 m as a default value.

The Calculator may be used in English, Spanish, Portuguese, French, or Dutch. The language can be changed using the Language drop-down in the upper left-hand corner of the Calculator. Regardless of the language chosen, the Calculator always uses a period ('.') as the decimal separator. If you would like to contribute labels for another language, please submit an issue to the Calculator GitHub repository.

The geographic coordinate north or south of the Equator (where latitude is 0) for the point of reference for the calculation, which is determined by the specific locality type. Latitudes north of the Equator are positive by convention, while latitudes to the south are negative. The minus sign ("−") should be included as appropriate. The Calculator supports degree-based geographic coordinate formats for latitude and longitude: decimal degrees (e.g. 35.3733333), degrees decimal minutes (e.g. 35° 22.4′ N) and degrees-minutes-seconds (e.g. 35° 22′ 24″ N).

The resulting latitude for a given calculation, in decimal degrees. Equivalent to the Darwin Core term decimalLatitude. See also, Input Latitude.

The pattern of the most specific part of a locality description to be georeferenced. The Calculator can compute georeferences for six basic locality types: Coordinates only, Geographic feature only, Distance only, Distance along a path, Distance along orthogonal directions, and Distance at a heading. Selecting a Locality Type will configure the Calculator to show all of the parameters that need to be set or chosen in order to do the georeference calculation. The Georeferencing Quick Reference Guide (Zermoglio et al. 2020) gives specific instructions for how to set the parameters for different examples of each of the locality types.

The geographic coordinate east or west of the prime meridian (an arc between the north and south poles where longitude is 0) for the point of reference for the calculation, which is determined by the specific locality type. Longitudes east of the prime meridian are positive by convention, while longitudes to the west are negative. The minus sign ("−") should be included as appropriate. The Calculator supports degree-based geographic coordinate formats for latitude and longitude: decimal degrees (−105.3733333), degrees decimal minutes (105° 22.4′ W), and degrees minutes seconds (105° 22′ 24″ W), .

The resulting longitude for a given calculation in decimal degrees. Equivalent to the Darwin Core term decimalLongitude. See also, Input Longitude.

Accounts for error associated with the ability to distinguish one point from another using any measuring tool, such as rulers on paper maps or the measuring tools on Google Maps or Google Earth. The units of the measurement must be the same as those for the locality description. The Distance Converter at the bottom of the Calculator is provided to aid in changing a measurement to the locality description units.

The linear distance from a point of origin. Offsets are used for the Locality Types "Distance at a heading" and "Distance only". If the Locality Type "Distance in orthogonal directions" is selected, there are two distinct offsets:

The feature is the place in the locality description that corresponds to the Input Latitude and Input Longitude. Types of features vary widely and include, for example, populated places, street addresses, junctions, crossings, lakes, mountains, parks, islands, etc. The geographic radial of the feature is the distance from the corrected center of the feature to the furthest point on the geographic boundary of that feature (see Extent of a Location in Georeferencing Best Practices (Chapman & Wieczorek 2020) and Radial of Feature in Georeferencing Quick Reference Guide (Zermoglio et al. 2020)).

The resulting combination of all sources of uncertainty (coordinate precision, unknown datum, data source, GPS accuracy, measurement error, feature geographic radial, distance precision, and heading precision) expressed as a linear distance – the radius in the point-radius method (Wieczorek et al. 2004). Along with the Output Latitude, Output Longitude, and Datum, the radius defines a smallest enclosing circle containing all of the possible places a locality description could mean.

Displayed in the bottom left-hand corner of the Calculator in the format yyyymmddll, where ll is the two-letter language code of the interface.

The closeness of an estimated value (for example, measured or computed) to a standard or accepted ("true") value. Antonym: inaccuracy. Compare error, bias, precision, false precision and uncertainty.

A measurement of the vertical distance above a vertical datum, usually mean sea level or geoid. For points on the surface of the earth, altitude is synonymous with elevation.

The meridian of longitude opposite a given meridian. A meridian and its antimeridian form a continuous ring around the Earth. The "Antimeridian" is the specific meridian of longitude opposite the prime meridian and is used as the rough basis of the International Date Line.

The difference between the average value of a set of measurements and the accepted true value. Bias is equivalent to the average systematic error in a set of measurements and a correction to negate the systematic error can be made by adjusting for the bias. Compare accuracy, error, precision, false precision and uncertainty.

The spatial divide between what is inside a location and what is outside of it.

An area defined by the coordinates of two diagonally opposite corners of a polygon, where those two corners define the north-south and east-west extremes of the area contained within.

see locality clause.

The format in which coordinates are encoded, such as "decimal degrees", "degrees minutes seconds", "degrees decimal minutes", or Universal Transverse Mercator (UTM).

The fraction of a degree corresponding to the number of significant digits in the source coordinates. For example, if the coordinates are reported to the nearest minute, the precision is 1/3600th (0.00027778) of a degree; if a decimal degree is reported to two decimal places, the precision is 0.01 of a degree.

(also spatial reference system) A coordinate system defined in relation to a standard reference or datum.

A geometric system that defines the nature and relationship of the coordinates it uses to uniquely define positions. Examples include the geographic coordinate system and the Universal Transverse Mercator (UTM) coordinate system.

A measure of the minimum distance on the surface from a coordinate within which a locality might be interpreted to be.

A set of values that define a position within a coordinate system. Coordinates are used to represent locations in space relative to other locations.

The Darwin Core term corresponding to the maximum uncertainty distance when given in meters.

The point within a location, or on its boundary, that minimizes the geographic radial of the location. This point is obtained by making the smallest enclosing circle that contains the entire feature, and then taking the center of that circle. If that center does not fall inside the boundaries of the feature, make the smallest enclosing circle that has its center on the boundary of the feature. Note that in the second case, the new circle, and hence the radial, will always be larger than the uncorrected one (see Polygons (Chapman & Wieczorek 2020)).

A standard for exchanging information about biological diversity (see Darwin Core).

‘Fitness for use’ of data (Juran 1964, Juran 1995, Chrisman 1991, Chapman 2005a). As the collector of the original data, you may have an intended use for the data you collect but data have the potential to be used in unforeseen ways; therefore, the value of your data is directly related to the fitness of those data for a variety of uses. As data become more accessible, many more uses become apparent (Chapman 2005c).

A set of one or more parameters that serve as a reference or basis for the calculation of other parameters ISO 19111. A datum defines the position of the origin, the scale, and the orientation of the axes of a coordinate system. For georeferencing purposes, a datum may be a geodetic datum or a vertical datum.

Degrees expressed as a single real number (e.g. −22.343456). Note that latitudes south of the equator are negative, as are longitudes west of the prime meridian to −180 degrees. See also decimal latitude and decimal longitude.

Latitude expressed in decimal degrees. The limits of decimal latitude are −90 to 90, inclusive.

Longitude expressed in decimal degrees. The limits of decimal longitude are −180 to 180, inclusive.

see magnetic declination.

see digital elevation model.

A measurement of the vertical distance below a vertical datum. In this document, we try to modify the term to signify the medium in which the measurement is made. Thus, "water depth" is the vertical distance below an air-water interface in a waterbody (ocean, lake, river, sinkhole, etc.). Compare distance above surface. Depth is always a non-negative number.

A digital representation of the elevation of locations on the surface of the earth, usually represented in the form of a rectangular grid (raster) that stores the elevation relative to mean sea level or some other known vertical datum. The term Digital Terrain Model (DTM) is sometimes used interchangeably with DEM, although it is usually restricted to models representing landscapes. A DTM usually contains additional surface information such as peaks and breaks in slope.

see heading.

In addition to elevation and depth, a measurement of the vertical distance above a reference point, with a minimum and a maximum distance to cover a range. For surface terrestrial locations, the reference point should be the elevation at ground level. Over a body of water (ocean, sea, lake, river, glacier, etc.), the reference point for aerial locations should be the elevation of the air-water interface, while the reference point for sub-surface benthic locations should be the interface between the water and the substrate. Locations within a water body should use depth rather than a negative distance above surface. Distances above a reference point should be expressed as positive numbers, while those below should be negative. The maximum distance above a surface will always be a number greater than or equal to the minimum distance above the surface. Since distances below a surface are negative numbers, the maximum distance will always be a number less than or equal to the minimum distance. Compare altitude.

Degrees, minutes and seconds – one of the most common formats for expressing geographic coordinates on maps. A degree is divided into 60 minutes of arc and each minute is divided into 60 seconds of arc. Degrees, minutes and seconds are denoted by the symbols °, ′, ″. Degrees of latitude are integers between 0 and 90, and should be followed by an indicator for the hemisphere (e.g. N or S). Degrees of longitude are integers between 0 and 180, and should be followed by an indicator for the hemisphere (e.g. E or W).

Within a coordinate reference system (e.g. as provided by a GPS or a map grid reference system), the line representing eastward distance from a reference meridian on a map.

A measurement of the vertical distance of a land or water surface above a vertical datum. On maps, the reference datum is generally some interpretation of mean sea level or the geoid, while in devices using GPS/GNSS, the reference datum is the ellipsoid of the geodetic datum to which the GPS unit is configured, though the device may make corrections to report the elevation above mean sea level or the geoid. Elevations that are above a reference point should be expressed as positive numbers, while those below should be negative. Compare depth, distance above surface, and altitude.

A three-dimensional, closed geometric shape, all planar sections of which are ellipses or circles. An ellipsoid has three independent axes. If an ellipsoid is made by rotating an ellipse about one of its axes, then two axes of the ellipsoid are the same, and it is called an ellipsoid of revolution. When used to represent a model of the earth, the ellipsoid is an oblate ellipsoid of revolution made by rotating an ellipse about its minor axis.

The entry point on the surface of the ocean or lake where a diver enters the water and from which all activities are measured. See Three-Dimensional Shapes (Chapman & Wieczorek 2020).

EPSG codes are defined by the International Association of Oil and Gas Producers, using a spatial reference identifier (SRID) to reference spatial reference systems. The EPSG Geodetic Parameter Dataset (IOPG 2019) is a collection of definitions of coordinate reference systems (including datums) and coordinate transformations which may be global, regional, national or local in application.

The difference between a computed, estimated, or measured value and the accepted true, specified, or theoretically correct value. It encompasses both the imprecision of a measurement and its inaccuracies. Error can be either random or systematic. If the error is systematic, it is called "bias". Compare accuracy, bias, precision, false precision and uncertainty.

A process occurring at a particular location during a period of time. Used generically to cover various kinds of collecting events, sampling events, and observations.

The entire space within the boundary a location actually represents. The extent can be a volume, an area, or a distance.

An artefact of recording data with a greater number of decimal places than implied by the original data. This often occurs following transformations from one unit or coordinate system to another, for example from feet to meters, or from degrees-minutes-and-seconds to decimal degrees. In general, precision cannot be conserved across metric transformations; however, in practice it is often recorded as such. For example, a record of 10°20’ stored in a database in decimal degrees is ~10.3°. When exported from some databases, it will result in a value of 10.3333333333 with a precision of 10 decimal places in degrees rather than the original precision of 1-minute. Misinterpreting the precision of the coordinate representation as a precision in distance on the ground, 10^-10 degrees corresponds to about 0.002 mm at the equator, while the precision of 1-minute corresponds to about 2.6 km. This is not a true precision as it relates to the original data, but a false precision as reported from a combination of the coordinate conversion and the representation of resulting fraction in the export from a database. Compare with precision and accuracy.

An object of observation, measurement, or reference that can be represented spatially. Often categorized into "feature types" (e.g. mountain, road, populated place, etc.) and given names for specific instances (e.g. "Mount Everest", "Ruta 40", "Istanbul"), which are also sometimes referred to as "named places", "place names" or "toponyms".

See shape. Note that "footprint" was used in some earlier georeferencing documents and in the Darwin Core term names footprintWKT and footprintSpatialFit.

An index of geographical features and their locations, often with geographic coordinates.

In geographic terms, refers to the conversion of a geographic representation to one with less resolution and less information content; traditionally associated with a change in scale. Also referred to as: fuzzying, dummying-up, etc. (Chapman 2020).

The process (verb) or product (noun) of determining the coordinates for a street address. It is also sometimes used as a synonym for georeference.

A coordinate reference system based on a geodetic datum, used to describe positions on the surface of the earth.

A mathematical model that uses a reference ellipsoid to describe the size and shape of the surface of the earth and adds to it the information needed for the origin and orientation of coordinate systems on that surface.

The representation in geographic coordinates of a vertical projection of a boundary onto a model of the surface of the earth.

The midpoint of the extremes of latitude and longitude of a feature. Geographic centers are relatively easy to determine, but they generally do not correspond to the center obtained by a least circumscribing circle. For that reason it is not recommended to use a geographic center for any application in georeferencing. Compare corrected center.

The part of a description of a location that consists of geographic coordinates and associated uncertainty. Non-geographic components of a location description include elevation, depth, and distance above surface.

A coordinate system that uses geographic coordinates.

A geodetic coordinate reference system that uses geographic coordinates.

A measurement of a location on the earth’s surface expressed as latitude and longitude.

The entire space within the geographic boundary of a location. The geographic extent can be an area or a distance.

A set of computer-based tools designed to capture, store, manipulate, analyse, map, manage, and present all types of geographical data and information in the form of maps.

The distance from the corrected center of a location to the furthest point on the geographic boundary of that location. The geographical radial is what contributes to calculations of the maximum uncertainty distance using the point-radius georeferencing method. The term geographic radial, as defined here, replaces its equivalent "extent" used in the early versions of these Best Practices and related documents, including the Georeferencing Quick Reference Guide (Wieczorek et al. 2012a) and versions of the Georeferencing Calculator (Wieczorek & Wieczorek 2018) and its Manual for the Georeferencing Calculator (Wieczorek & Bloom 2015) before 2019, while the new definition of extent as found in this document remains more in keeping with common usage and understanding and has also been updated in the latest versions of the Georeferencing Quick Reference Guide (Zermoglio et al. 2020) and in this Manual.

A global equipotential surface that approximates mean sea level. This surface is everywhere perpendicular to the force of gravity (Loweth 1997).

The measures and properties of points, lines, and surfaces. Geometry is used to represent the geographic component of locations.

The process (verb) or product (noun) of interpreting a locality description into a spatially mappable representation using a georeferencing method. Compare with geocode. The usage here is distinct from the concept of georeferencing satellite and other imagery (known as georectification).

The type of spatial representation produced as the output of a georeferencing protocol. In this document we discuss three particular methods of representation in detail, the shape method, the bounding box method, and the point-radius method.

The documented specific steps to apply to a locality, based on the locality type, to produce a particular type of spatial representation.

see geographic information system.

Globally Unique Identifier, a 128-bit string of characters applied to one and only one physical or digital entity so that the string uniquely identifies the entity and can be used to refer to the entity. See also persistent identifier (PID).

Global Navigation Satellite System, the generic term for satellite navigation systems that provide global autonomous geo-spatial positioning. This term encompasses GPS, GLONASS, Galileo, BeiDou and other regional systems.

Global Positioning System, a satellite-based system used for determining positions on or near the earth. Orbiting satellites transmit radio signals that allow a receiver to calculate its own location as coordinates and elevation, sometimes with accuracy estimates. A GPS or GNSS Receiver (including those in smartphones and cameras) is the instrument that receives the radio signals and translates them into geographic coordinates. See also GNSS of which GPS is one example.

The colloquial term used to refer to both GPS and GNSS receivers. A GPS or GNSS receiver is an instrument which, in combination with an inbuilt or separate antenna, is able to receive and interpret signals from GNSS satellites.

a network or array of evenly spaced orthogonal lines used to organize space into partitions. Often these are superimposed on a map and used for reference, such as Universal Transverse Mercator (UTM) grid.

the location on the land surface directly above a radiolocation point in a cave where the magnetic radiation lines are vertical. See Elevation (Chapman & Wieczorek 2020).

see Globally Unique Identifier.

Compass direction such as east or northwest, or sometimes given as degrees clockwise from north. Usually used in conjunction with offset to give a distance and direction from a feature.

see vertical datum.

The angular distance of a point north or south of the equator.

The verbal representation of a location, also sometimes called "locality description".

A part of a locality description that can be categorized into one of the locality types, to which a specific georeferencing method can be applied.

A category applied to a locality clause that determines the specific georeferencing method that should be applied.

A physical space that can be positioned and oriented relative to a reference point, and potentially described in a natural language locality description. In georeferencing, a location can have distinct representations based on distinct rules of interpretation, each of which is embodied in a georeferencing method.

The angular distance of a point east or west of a prime meridian at a given latitude.

The angle on the horizontal plane between magnetic north (the direction the north end of a magnetized compass needle points, corresponding to the direction of the Earth’s magnetic field lines) and true north (the direction along a meridian towards the geographic North Pole). This angle varies depending on the position on the Earth’s surface and changes over time.

The radius in a point-radius representation of a location, that is a numerical value that defines the upper limit of the horizontal distance from the position of the given geographic coordinate to a point on the outer extremity of the geographic area within which the whole of a location lies. When given in meters, it corresponds to the Darwin Core term coordinateUncertaintyInMeters.

A vertical datum from which heights such as elevation are usually measured. Mean sea levels were traditionally determined locally by measuring the midpoint between a mean low and mean high tide at a particular location averaged over a 19-year period covering a complete tidal cycle. More recently, MSL is best described by a geoid.

A line on the surface of the earth where all of the locations have the same longitude. Compare antimeridian and prime meridian.

see feature. Note that "named place" was used in some earlier georeferencing documents.

Within a coordinate reference system (e.g. as provided by a GPS or a map grid reference system), the line representing northward distance from a reference latitude.

A displacement from a reference location. Usually used in conjunction with heading to give a distance and direction from a feature.

A route or track between one place and another. In some cases the path may cross itself.

A long-lasting reference to a document, file, web page, or other object. The term "persistent identifier" is usually used in the context of digital objects accessible over the Internet. There are many options for PIDs, such as Globally Unique Identifiers (GUIDs), Digital Object Identifiers (DOIs), and Universal Unique Identifiers (UUIDs).

A representation of the geographic component of a location as a geographic coordinate and a maximum uncertainty distance. The point-radius georeferencing method produces georeferences that include geographic coordinates, a coordinate reference system, and a maximum uncertainty distance that encompasses all of the possible geographic coordinates where a locality might be interpreted to be. This representation encompasses all of the geographical uncertainties within a circle. The point-radius method uses ranges to represent the non-geographic descriptors of the location (elevation, depth, distance above surface).

The set of locations with longitude designated as 0 degrees east and west, to which all other longitudes are referenced. The Greenwich meridian is internationally recognized as the prime meridian for many popular and official purposes.

A series of transformations that convert the locations of points in a coordinate reference system on a curved surface (the reference surface or datum) to the locations of corresponding points in a coordinate reference system on a flat plane. The datum is an integral part of the projection, as projected coordinate systems are based on geographic coordinates, which are in turn referenced to a geodetic datum. It is possible, and even common for datasets to be in the same projection, but referenced to distinct geodetic datums, and therefore have different coordinate values.

see data quality.

The distance from a center point (e.g. the corrected or geographic center) within a location to the furthest point on the outermost boundary of that location. See also geographic radial.

The process of returning something to the source from which it was extracted. In the georeferencing sense, this refers to the process of adding the results of georeferencing to the original data, especially when georeferencing was done by a third party.

A documented set of steps to take in order to produce a standardized representation of source information.

A civil aviation safety-critical system that supports wide-area or regional augmentation through the use of geostationary (GEO) satellites that broadcast the augmentation information (see discussion in Satellite Based Augmentation System (Chapman & Wieczorek 2020)).

Synonym of footprint. A representation of the geographic component of a location as a geometry. The result of a shape georeferencing method includes a shape as the geographic component of the georeference, which contains the set of all possible geographic coordinates where a location might be interpreted to be. This representation encompasses all of the geographical uncertainties within the geometry given. The shape method uses ranges to represent the non-geographic descriptors of the location (elevation, depth, distance above surface).

a circle with the smallest radius (radial) that contains all of a given set of points (or a given shape) on a surface (see Smallest-circle problem). This is seldom the same as the geographic center, nor the midpoint between two most distant geographic coordinates of a location.

a measure of how well one geometric representation matches another geometric representation as a ratio of the area of the larger of the two to the area of the smaller one. (See Determining Spatial Fit (Chapman & Wieczorek 2020)).

see coordinate reference system.

A local outcrop or series of adjacent outcrops that display a vertical sequence of strata in the order they were deposited.

A path along which observations, measurements, or samples are made. Transects are often recorded as a starting location and a terminating location.

A surveyed reference point, often on high points of elevation (mountain tops, etc.) and usually designated with a fixed marker on a small pyramidal structure or a pillar. The exact location is determined by survey triangulation and hence the alternative names "trigonometrical point", "triangulation point" or "benchmark".

A measure of the incompleteness of one’s knowledge or information about an unknown quantity whose true value could be established if complete knowledge and a perfect measuring device were available (Cullen & Frey 1999). Georeferencing methods codify how to incorporate uncertainties from a variety of sources (including accuracy and precision) in the interpretation of a location. Compare accuracy, error, bias, precision, and false precision.

A standardized coordinate system based on a metric rectangular grid system and a division of the earth into sixty 6-degree longitudinal zones. The scope of UTM covers from 84° N to 80° S. (See Universal Transverse Mercator (UTM) Coordinates (Chapman & Wieczorek 2020)).

A reference surface for vertical positions, such as elevation. Vertical datums fall into several categories, including: tidal, based on sea level; gravimetric, based on a geoid; geodetic, based on ellipsoid models of the Earth; or local, based on a local reference surface. Also known as height datum.

An air navigation aid developed by the US Federal Aviation Administration to augment the Global Positioning System (GPS), with the goal of improving its accuracy, integrity, and availability. See also SBAS, of which WAAS is one example.

World Geodetic System 1984, a popular globally-used horizontal geodetic coordinate reference system (EPSG:4326) upon which raw GPS measurements are based (though a GPS receiver is capable of delivering coordinates in other reference systems). The term is also commonly used for the geodetic datum used by that system and for the ellipsoid (EPSG:7030) upon which that datum (EPSG:6326) is based.