ISO 6709

ISO 6709 Standard representation of geographic point location by coordinates is the international standard for representation of latitude, longitude and altitude for geographic point locations.

The first edition (ISO 6709:1983) was developed by ISO/IEC JTC 1/SC 32. Later the standard was transferred to ISO/TC211, Geographic information/Geomatics in 2001. The committee completely revised the second edition (ISO 6709:2008). There was a short technical corrigendum (ISO 6709:2008/Cor 1:2009) released in 2009.[1]

The second edition consists of a main part and eight annexes (Annexes A through H). The main part and Annexes A and C give encoding-independent general rules to define items to specify geographic point(s). Annex D suggests a display style for human interface. Annexes F and G suggest styles of XML expression. Annex H suggests string expression, which supersedes the first edition of the standard.

General rules

Items

A geographical point is specified by the following four items:

  • First horizontal coordinate (y), such as latitude (negative number south of equator and positive north of equator)
  • Second horizontal coordinate (x), such as longitude (negative values west of Prime Meridian and positive values east of Prime Meridian)
  • Vertical coordinate, i.e. height or depth (optional)
  • Identification of coordinate reference system (CRS) (optional)

The first three items are numerical values called coordinates. The CRS gives the relationship between the coordinates and a point on the earth. The identification of CRS could be a full description of properties defined in ISO 19111; only an identifier given by some registry (such as EPSG) is used in most cases, since only such identification is enough for most information exchange purposes.

Order, sign, and units

Order, positive direction, and units of coordinates are supposed to be defined by the CRS. When CRS identification is missing, the data must be interpreted by the following conventions:

  • Latitude comes before longitude
  • North latitude is positive
  • East longitude is positive
  • Fraction of degrees is preferred in digital data exchange, while sexagesimal notation is tolerated for compatibility

There is no such interpretation rule for vertical coordinates.

Representation at the human interface (Annex D)

When there is no guideline given from the user community, the following styles are suggested:

  1. Coordinate values (latitude, longitude, and altitude) should be delimited by spaces.
  2. The decimal point is a part of the value, thus must usually be configured by the operating system.[2]
  3. Multiple points should be represented by multiple lines.
  4. Latitude and longitude should be displayed by sexagesimal fractions (i.e. minutes and seconds).
  5. When minutes and seconds are less than ten, leading zeroes should be shown.
  6. Degree, minutes and seconds should be followed by the symbols ° (U+00B0), ′ (U+2032), and ″ (U+2033), without spaces between the number and symbol.
  7. North and south latitudes should be indicated by N and S following immediately after the digits.
  8. East and west longitudes should be indicated by E and W following immediately after the digits.
  9. Units of elevation or depth should be given by symbols, immediately after the digits.[3]
  10. Elevation below reference level or depth above reference level should be indicated by a minus sign − (U+2212).

Examples:

  • 50°40′46,461″N 95°48′26,533″W 123,45m
  • 50°03′46.461″S 125°48′26.533″E 978.90m

XML representation (Annex F)

The XML representation based on the conceptual model of Annex C uses XML namespace http://www.isotc211.org/2006/gpl. However, there is no published XML schema at the time of writing (August 2011).

<gpl:GPL_CoordinateTuple xmlns:gpl="http://www.isotc211.org/gpl">
  <gpl:tuple srsName="urn:ogc:def:crs:EPSG:6.6:4326">
    35.89421911 139.94637467
  </gpl:tuple>
</gpl:GPL_CoordinateTuple>

String expression (Annex H)

A string expression of a point consists of latitude, longitude, height or depth, CRS identifier, and trailing solidus (/) without any delimiting character. When height or depth is used, there must be CRS identifier.[4]

Latitude

Latitude is a number preceded by a sign character. A plus sign (+) denotes northern hemisphere or the equator, and a minus sign (-) denotes southern hemisphere.[5]

The integer part of the number is a fixed length. The number of digits in that part indicates the units, thus leading zero(es) must be filled when necessary. The fractional part must have the appropriate number of digits to represent the required precision of the coordinate.

num. digits units format example
2 deg ±DD.D +40.20361
4 deg, min ±DDMM.M +4012.22
6 deg, min, sec ±DDMMSS.S +401213.1

Longitude

Longitude is a number preceded by a sign character. A plus sign (+) denotes east longitude or the prime meridian, and a minus sign (-) denotes west longitude or 180° meridian (opposite of the prime meridian).[6]

Rules about the number of digits are the same as for latitude.

num. digits units format example
3 deg ±DDD.D -075.00417
5 deg, min ±DDDMM.M -07500.25
7 deg, min, sec ±DDDMMSS.S -0750015.1

Height or depth

  • When height or depth is present, CRS identifier must follow.
  • Positive direction and units are defined by CRS.[7]
  • Negative number does not necessarily mean position below reference level.
  • Positive is up for height, negative for depth.

CRS identifier

The CRS identifier begins with "CRS". There are three styles:

  1. When a registry provides online resolver, CRS<url>
  2. When a registry is offline, CRSregistry:crsid
  3. When the data creator provides full definition of CRS using ISO 19111, CRS<CRSID>

The example of original Annex H always use "CRSWGS_84".

Examples

Notes

  1. ^ "ISO 6709:2008/Cor 1:2009 -". ISO. Retrieved 8 June 2016.
  2. ^ Probably the intention is that the locale environment should not be overridden.
  3. ^ This is different from SI style guides
  4. ^ Height without CRS identifier was allowed in the first edition, but not today. Ending with longitude is still allowed.
  5. ^ Annex H allows letters N and S as sign characters, but gives no examples.
  6. ^ Annex H allows letters E and W as sign characters, but gives no examples.
  7. ^ This is different from the 1983 edition.

See also

External links

Standards

Implementations

Discrete Global Grid

A Discrete Global Grid (DGG) is a mosaic which covers the entire Earth's surface.

Mathematically it is a space partitioning: it consists of a set of non-empty regions that form a partition of the Earth's surface. In a usual grid-modeling strategy, to simplify position calculations, each region is represented by a point, abstracting the grid as a set of region-points. Each region or region-point in the grid is called a cell.

When each cell of a grid is subject to a recursive partition, resulting in a "series of discrete global grids with progressively finer resolution", forming a hierarchical grid, it is named Hierarchical DGG (sometimes "DGG system").

Discrete Global Grids are used as the geometric basis for the building of geospatial data structures. Each cell is related with data objects or values, or (in the hierarchical case) may be associated with other cells. DGGs have been proposed for use in a wide range of geospatial applications, including vector and raster location representation, data fusion, and spatial databases.The most usual grids are for horizontal position representation, using a standard datum, like WGS84. In this context, it is common also to use a specific DGG as foundation for geocoding standardization.

In the context of a spatial index, a DGG can assign unique identifiers to each grid cell, using it for spatial indexing purposes, in geodatabases or for geocoding.

ED50

ED50 ("European Datum 1950") is a geodetic datum which was defined after World War II for the international connection of geodetic networks.

Geo (microformat)

Geo is a microformat used for marking up WGS84 geographical coordinates (latitude;longitude) in (X)HTML. Although termed a "draft" specification, this is a formality, and the format is stable and in widespread use; not least as a sub-set of the published hCalendar and hCard microformat specifications, neither of which is still a draft.Use of Geo allows parsing tools (for example other websites, or Firefox's Operator extension) to extract the locations, and display them using some other website or mapping tool, or to load them into a GPS device, index or aggregate them, or convert them into an alternative format.

Geo URI scheme

The geo URI scheme is a Uniform Resource Identifier (URI) scheme defined by the Internet Engineering Task Force's RFC 5870 (published 8 June 2010) as:

a Uniform Resource Identifier (URI) for geographic locations using the 'geo' scheme name. A 'geo' URI identifies a physical location in a two- or three-dimensional coordinate reference system in a compact, simple, human-readable, and protocol-independent way.

The current revision of the vCard specification supports geo URIs in a vCard's "GEO" property, and the GeoSMS standard uses geo URIs for geotagging SMS messages. Android based devices support geo URIs, although that implementation is based on a draft revision of the specification, and supports a different set of URI parameters and query strings.

A geo URI is not to be confused with the site GeoUrl (which implements ICBM address).

Geodetic Reference System 1980

The Geodetic Reference System 1980 (GRS 80) is a geodetic reference system consisting of a global reference ellipsoid and a gravity field model.

Geodynamics

Geodynamics is a subfield of geophysics dealing with dynamics of the Earth. It applies physics, chemistry and mathematics to the understanding of how mantle convection leads to plate tectonics and geologic phenomena such as seafloor spreading, mountain building, volcanoes, earthquakes, faulting and so on. It also attempts to probe the internal activity by measuring magnetic fields, gravity, and seismic waves, as well as the mineralogy of rocks and their isotopic composition. Methods of geodynamics are also applied to exploration of other planets.

Irish grid reference system

The Irish grid reference system is a system of geographic grid references used for paper mapping in Ireland (both Northern Ireland and the Republic of Ireland). The Irish grid partially overlaps the British grid, and uses a similar co-ordinate system but with a meridian more suited to its westerly location.

Israeli Transverse Mercator

Israeli Transverse Mercator (Hebrew: רשת ישראל החדשה‎ Reshet Yisra'el Ha-Ḥadasha; ITM) is the new geographic coordinate system for Israel. The name is derived from the Transverse Mercator projection it uses and the fact that it is optimized for Israel. ITM has replaced the old coordinate system ICS. This coordinate system is sometimes also referred as the "New Israeli Grid". It has been use since January 1, 1994.

LOC record

In the Domain Name System, a LOC record (experimental RFC 1876) is a means for expressing geographic location information for a domain name.

It contains WGS84 Latitude, Longitude and Altitude (ellipsoidal height) information together with host/subnet physical size and location accuracy. This information can be queried by other computers connected to the Internet.

List of geocoding systems

This is a list of geocoding systems, in the sense of schemes that assign systematic labels to geographic entities.

This is not a list of software systems that can perform geocoding in the sense of turning a geographic name into a latitude and longitude.

Some of these code systems are free for use, others have different licences.

North American Datum

The North American Datum (NAD) is the datum now used to define the geodetic network in North America. A datum is a formal description of the shape of the Earth along with an "anchor" point for the coordinate system. In surveying, cartography, and land-use planning, two North American Datums are in use: the North American Datum of 1927 (NAD 27) and the North American Datum of 1983 (NAD 83). Both are geodetic reference systems based on slightly different assumptions and measurements.

North American Vertical Datum of 1988

The North American Vertical Datum of 1988 (NAVD 88) is the vertical datum for orthometric heights established for vertical control surveying in the United States of America based upon the General Adjustment of the North American Datum of 1988.

NAVD 88 was established in 1991 by the minimum-constraint adjustment of geodetic leveling observations in Canada, the United States, and Mexico. It held fixed the height of the primary tide gauge benchmark (surveying), referenced to the International Great Lakes Datum of 1985 local mean sea level (MSL) height value, at Rimouski, Quebec, Canada. Additional tidal bench mark elevations were not used due to the demonstrated variations in sea surface topography, i.e., that MSL is not the same equipotential surface at all tidal bench marks.

The definition of NAVD 88 uses the Helmert orthometric height, which calculates the location of the geoid (which approximates MSL) from modeled local gravity. The NAVD 88 model is based on then-available measurements, and remains fixed despite later improved geoid models.

NAVD 88 replaced the National Geodetic Vertical Datum of 1929 (NGVD 29), previously known as the Sea Level Datum of 1929. The elevation difference between points in a local area will show negligible change from one datum to the other, even though the elevation of both does change. NGVD 29 used a simple model of gravity based on latitude to calculate the geoid and did not take into account other variations. Thus, the elevation difference for points across the country does change between datums.

PZ-90

PZ-90 (short for Parametry Zemli 1990 goda, in Russian: Параметры Земли 1990 года) is a geodetic datum defined for use in the GLONASS system.PZ-90 uses ellipsoid parameters that are linked to the SK-42 reference system.

Sea Level Datum of 1929

The Sea Level Datum of 1929 was the vertical datum established for vertical control surveying in the United States of America by the General Adjustment of 1929. The datum was used to measure elevation (altitude) above, and depression (depth) below, mean sea level (MSL).

Mean sea level was measured at 26 tide gauges: 21 in the United States and 5 in Canada. The datum was defined by the observed heights of mean sea level at the 26 tide gauges and by the set of elevations of all bench marks resulting from the adjustment of observations. The adjustment required a total of 66,315 miles (106,724 km) of leveling with 246 closed circuits and 25 circuits at sea level.

Since the Sea Level Datum of 1929 was a hybrid model, it was not a pure model of mean sea level, the geoid, or any other equipotential surface. Therefore, it was renamed the National Geodetic Vertical Datum of 1929 (NGVD 29) in 1973. NGVD29 was superseded by the North American Vertical Datum of 1988 (NAVD 88), based upon an equipotential definition and a readjustment, although many cities and U.S. Army Corps of Engineers projects with established data continued to use the older datum.

South American Datum

The South American Datum (SAD) is a regional geodesic datum for South America. It was established in Brazil by SIRGAS 2000, and was made official in 2005.

Space geodesy

Space geodesy is geodesy by means of sources external to Earth, mainly artificial satellites (in satellite geodesy) but also quasars (in very-long-baseline interferometry, VLBI) and the retroreflectors on the Moon (in lunar laser ranging, LLR).

Tonal system

The Tonal system is a base 16 system of notation (predating the widespread use of hexadecimal in computing), arithmetic, and metrology proposed in 1859 by John W. Nystrom. In addition to new weights and measures, his proposal included a new calendar with sixteen months, a new system of coinage, and a clock with sixteen major divisions of the day (called tims). Nystrom advocated his system thus:

I am not afraid, or do not hesitate, to advocate a binary system of arithmetic and metrology. I know I have nature on my side; if I do not succeed to impress upon you its utility and great importance to mankind, it will reflect that much less credit upon our generation, upon scientific men and philosophers.

Vertical position

Vertical position or vertical location is a position along a vertical direction above or below a given vertical datum.

Vertical distance or vertical separation is the distance between two vertical positions.

Many vertical coordinates exist for expressing vertical position: depth, height, altitude, elevation, etc.

Each quantity may be expressed in various units: metres, feet, etc.

ISO standards by standard number
1–9999
10000–19999
20000+

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