ISO/PRF 6709

Standard representation of geographic point location by coordinates

Représentation normalisée de la localisation des points géographiques par coordonnées

General Information

• Status: Published
• ICS: 35.240.70 - IT applications in science
• Technical Committee: ISO/TC 211 - Geographic information/Geomatics
• Drafting Committee: ISO/TC 211/WG 9 - Information management
• Current Stage: 5060 - Close of voting Proof returned by Secretariat
• Completion Date: 16-Dec-2021

RELATIONS

• Consolidates: ISO/TS 28038:2018 - Determination and use of polynomial calibration functions
• Effective Date: 06-Jun-2022
• Replaces: ISO 6709:2008 - Standard representation of geographic point location by coordinates
• Effective Date: 15-Dec-2017

Standards Content (sample)

INTERNATIONAL ISO
STANDARD 6709
Third edition
Standard representation of geographic
point location by coordinates
Représentation normalisée de la localisation des points
géographiques par coordonnées
PROOF/ÉPREUVE
Reference number
ISO 6709:2021(E)
© ISO 2021
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ISO 6709:2021(E)
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© ISO 2021

All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may

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Published in Switzerland
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ISO 6709:2021(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

Introduction .............................................................................................................................................................................................................................. vi

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ..................................................................................................................................................................................... 1

3 Terms and definitions .................................................................................................................................................................................... 1

4 Abbreviated terms and character code notations ........................................................................................................... 4

4.1 Abbreviated terms .............................................................................................................................................................................. 4

4.2 Character code notations .............................................................................................................................................................. 5

5 Conformance ............................................................................................................................................................................................................ 5

6 Geographic point location (GPL) representation............................................................................................................... 5

6.1 Overview ...................................................................................................................................................................................................... 5

6.2 Component representation .......................................................................................................................................................... 6

6.3 Coordinate tuple.................................................................................................................................................................................... 6

6.4 Character string delimiters and terminator notation ......................................................................................... 7

6.5 CRS identifier structure ................................................................................................................................................................. 8

6.6 Text string representation ........................................................................................................................................................ 10

6.6.1 Background .......................................................................................................................................................................... 10

6.6.2 Formatting rules for angular measures ..................................................................................................... 10

6.6.3 Component structure ..................................................................................................................................................12

7 Human-readable GPL representation .........................................................................................................................................15

7.1 Overview of human-readable GPL representation .............................................................................................. 15

7.2 General requirements of human-readable GPL representation ............................................................... 16

7.3 Formatted examples of human-readable text strings ...................................................................................... 18

Annex A (normative) Conformance and abstract test suite .....................................................................................................20

Annex B (normative) Backwards compatible representation of geographic point location ................23

Annex C (informative) Uniqueness of latitude and longitude coordinates ..............................................................29

Annex D (informative) Latitude and longitude resolution........................................................................................................31

Annex E (informative) Changes compared to ISO 6709:2008 ................................................................................................32

Annex F (normative) Character encodings ................................................................................................................................................34

Bibliography .............................................................................................................................................................................................................................36

iii
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ISO 6709:2021(E)
Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards

bodies (ISO member bodies). The work of preparing International Standards is normally carried out

through ISO technical committees. Each member body interested in a subject for which a technical

committee has been established has the right to be represented on that committee. International

organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.

ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of

electrotechnical standardization.

The procedures used to develop this document and those intended for its further maintenance are

described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the

different types of ISO documents should be noted. This document was drafted in accordance with the

editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of

any patent rights identified during the development of the document will be in the Introduction and/or

on the ISO list of patent declarations received (see www.iso.org/patents).

Any trade name used in this document is information given for the convenience of users and does not

constitute an endorsement.

For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and

expressions related to conformity assessment, as well as information about ISO's adherence to

the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see

www.iso.org/iso/foreword.html.

This document was prepared by Technical Committee ISO/TC 211, Geographic information/Geomatics,

in collaboration with the European Committee for Standardization (CEN) Technical Committee CEN/TC

287, Geographic Information, in accordance with the Agreement on technical cooperation between ISO

and CEN (Vienna Agreement).

This third edition cancels and replaces the second edition (ISO 6709:2008), which has been technically

revised. It also incorporates the Technical Corrigendum ISO 6709:2008/Cor. 1:2009.

The main changes are as follows:
— Harmonization with other recently revised ISO/TC 211 International Standards;

— Clarification of normative requirements to maintain rigid backwards compatibility when required;

— Correction of the issues contained in the Technical Corrigendum ISO 6709:2008/Cor. 1:2009;

— Correction of annexes that contained normative requirements but were labelled as informative;

— Deletion of annexes and concepts which have changed and were no longer suitable for the revised

edition;

— Correction of instances where European numeric formatting conventions were incorrectly inserted.

These conventions will no longer be recommended;
— Clarification of editorial issues.

Any feedback or questions on this document should be directed to the user’s national standards body. A

complete listing of these bodies can be found at www.iso.org/members.html.

In accordance with the ISO/IEC Directives, Part 2, 2018, Rules for the structure and drafting of

International Standards, in International Standards the decimal sign is a comma on the line. However,

the General Conference on Weights and Measures (Conférence Générale des Poids et Mesures) at its

meeting in 2003 passed unanimously the following resolution:
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ISO 6709:2021(E)
“The decimal marker shall be either a point on the line or a comma on the line.”

In practice, the choice between these alternatives depends on customary use in the language concerned.

In the technical areas of geodesy and geographic information it is customary for the decimal point

always to be used, for all languages. That practice is used throughout this document.

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ISO 6709:2021(E)
Introduction

Geographic point location (GPL) is the description of a well-defined geographic place using a single

coordinate tuple. Efficient interchange of GPL data requires formats which are universally interpretable

and which allow the identification of points on, above and below the Earth’s surface. Users in various

disciplines have different requirements. This is exemplified by the use of degrees and decimal degrees,

as well as the traditional degrees, minutes and seconds, for recording latitude and longitude. User

applications can also require various levels of precision and can use latitude and longitude without

height.

ISO 6709:1983 defined a specific format representation of latitude and longitude, and optionally

altitude.
ISO 6709:2008 revised the format representation of the 1983 edition by:

— adding the ability to identify the coordinate reference system (CRS) to which coordinates are

referenced, without which location is ambiguous, and

— expanding the use of altitude to allow for any ellipsoidal or gravity-related height or depth.

Since the first edition of this document in 1983, the field of geodesy has undergone significant

technological advances, along with the continued development of other related geodesy and geomatics

standards.

The aim of this edition is to address these new advances and standards and to revise the coordinate

string suitable for digital representation (Clause 6) while continuing to support the requirements of the

previous edition (Annex B).

Clause 7 defines a simpler structure for the unambiguous representation of GPL in a human-readable

format.
In addition, a series of annexes are provided with the following content:

— Annex A (normative) defines the abstract test suite used for conformance testing;

— Annex B (normative) defines the representation of latitude and longitude coordinates that maintain

backwards compatibility with ISO 6709:2008;

— Annex C (informative) presents a description and examples of how the position of coordinates can

appear ambiguous without the use of a CRS;

— Annex D (informative) presents a table of mathematical precision values of resolution for latitude

and longitude;

— Annex E (informative) describes the changes in this document compared to the previous edition of

ISO 6709;

— Annex F (normative) specifies encodings for character strings and delimiters required in this

document.
The following options are highlighted to users of this document:

a) For all cases where backwards compatibility is not required, this document recommends using

the methods and rules specified in Clause 6, GPL representation, or Clause 7, human-readable GPL

representation;

b) However, in systems and environments where backwards compatibility with ISO 6709:2008 is

required, the methods and rules specified in Annex B can be used.

In addition, when using Annex B, it is recommended that suitable and comprehensive ancillary

documentation, not defined within this document or in previous editions of this document, be

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prepared and accompany all instances of geographic point location text strings and human-readable

representations claiming backwards compatibility.
The use of this document:

— establishes an expanded point representation string format supporting the current concepts and

standards of geodesy and geographic information;

— when required, continues to support the needs of established user communities by maintaining

backwards compatibility with the previous edition of this document (ISO 6709:2008);

— reduces the cost of interchange of data;

— reduces the delay in converting non-standard coding structures in preparation for interchange by

providing advance knowledge of the standard interchange format; and
— provides flexible support for geographic point representation.
vii
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INTERNATIONAL STANDARD ISO 6709:2021(E)
Standard representation of geographic point location by
coordinates
1 Scope

This document specifies the representation of latitude and longitude and optionally height or depth

compatible with previous editions of ISO 6709.

This document also supports the representations of other coordinate types and time that can be

associated with those coordinates as defined through one or more coordinate reference systems (CRS).

This document describes a text string of coordinates, suitable for electronic data exchange, for

one point, including reference system identification to ensure that the coordinates unambiguously

represent the position of that point. Files containing multiple points with a single common reference

system identification are out of scope. This document also describes a simpler text string structure for

coordinate representation of a point location that is more suitable for human readability.

2 Normative references

The following documents are referred to in the text in such a way that some or all of their content

constitutes requirements of this document. For dated references, only the edition cited applies. For

undated references, the latest edition of the referenced document (including any amendments) applies.

ISO 8601-1, Date and time — Representations for information interchange — Part 1: Basic rules

ISO 8601-2, Date and time — Representations for information interchange — Part 2: Extensions

ISO/IEC 10646:2020, Information technology — Universal coded character set (UCS)
ISO 19111, Geographic information — Referencing by coordinates

ISO 19162, Geographic information — Well-known text representation of coordinate reference systems

3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
accuracy

closeness of agreement between a test result or measurement result and the true value

[SOURCE: ISO 3534-2:2006, 3.1.1, modified — Notes to entry have been removed.]
3.2
altitude
height where the chosen reference surface is mean sea level
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3.3
compound coordinate reference system

coordinate reference system using at least two independent coordinate reference systems

Note 1 to entry: Coordinate reference systems are independent of each other if coordinate values in one cannot

be converted or transformed into coordinate values in the other.
[SOURCE: ISO 19111:2019, 3.1.3]
3.4
coordinate
one of a sequence of numbers designating the position of a point

Note 1 to entry: In a spatial coordinate reference system, the coordinate numbers are qualified by units.

[SOURCE: ISO 19111:2019, 3.1.5]
3.5
coordinate reference system
coordinate system that is related to an object by a datum

Note 1 to entry: Geodetic and vertical datums are referred to as reference frames.

Note 2 to entry: For geodetic and vertical reference frames, the object will be the Earth. In planetary applications,

geodetic and vertical reference frames may be applied to other celestial bodies.
[SOURCE: ISO 19111:2019, 3.1.9]
3.6
coordinate set

collection of coordinate tuples referenced to the same coordinate reference system and if that

coordinate reference system is dynamic also to the same coordinate epoch
[SOURCE: ISO 19111:2019, 3.1.10]
3.7
coordinate system

set of mathematical rules for specifying how coordinates are to be assigned to points

[SOURCE: ISO 19111:2019, 3.1.11]
3.8
coordinate tuple
tuple composed of coordinates

Note 1 to entry: The number of coordinates in the coordinate tuple equals the dimension of the coordinate

system; the order of coordinates in the coordinate tuple is identical to the order of the axes of the coordinate

system.
[SOURCE: ISO 19111:2019, 3.1.13]
3.9
datum
reference frame

parameter or set of parameters that realize the position of the origin, the scale, and the orientation of a

coordinate system
[SOURCE: ISO 19111:2019, 3.1.15]
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3.10
depth

distance of a point from a chosen vertical reference surface downward along a line that is perpendicular

to that surface

Note 1 to entry: The line direction may be straight or be dependent on the Earth's gravity field or other physical

phenomena.

Note 2 to entry: A depth above the vertical reference surface will have a negative value.

[SOURCE: ISO 19111:2019, 3.1.17]
3.11
ellipsoidal height
geodetic height

distance of a point from the reference ellipsoid along the perpendicular from the reference ellipsoid to

this point, positive if upwards or outside of the reference ellipsoid

Note 1 to entry: Only used as part of a three-dimensional ellipsoidal coordinate system or as part of a three-

dimensional Cartesian coordinate system in a three-dimensional projected coordinate reference system, but

never on its own.
[SOURCE: ISO 19111:2019, 3.1.24]
3.12
geographic point location
well defined geographic place described by one coordinate tuple
[SOURCE: ISO 19145:2013, 4.1.11]
3.13
geographic point location representation
syntactic description of a geographic point location in a well known format
[SOURCE: ISO 19145:2013, 4.1.12]
3.14
gravity-related height
height that is dependent on the Earth’s gravity field

Note 1 to entry: This refers to, amongst others, orthometric height and Normal height, which are both

approximations of the distance of a point above the mean sea level, but also may include Normal-orthometric

heights, dynamic heights or geopotential numbers.

Note 2 to entry: The distance from the reference surface may follow a curved line, not necessarily straight, as it is

influenced by the direction of gravity.
[SOURCE: ISO 19111:2019, 3.1.37]
3.15
height

distance of a point from a chosen reference surface positive upward along a line perpendicular to that

surface

Note 1 to entry: A height below the reference surface will have a negative value.

Note 2 to entry: Generalization of ellipsoidal height (h) and gravity-related height (H).

[SOURCE: ISO 19111:2019, 3.1.38]
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3.16
measurement precision
precision

closeness of agreement between indications or measured quantity values obtained by replicate

measurements on the same or similar objects under specified conditions

Note 1 to entry: Measurement precision is usually expressed numerically by measures of imprecision, such as

standard deviation, variance, or coefficient of variation under the specified conditions of measurement.

Note 2 to entry: The "specified conditions" can be, for example, repeatability conditions of measurement,

intermediate precision conditions of measurement, or reproducibility conditions of measurement (see

ISO 5725-1:1994).

Note 3 to entry: Measurement precision is used to define measurement repeatability, intermediate measurement

precision, and measurement reproducibility.

Note 4 to entry: Sometimes "measurement precision" is erroneously used to mean measurement accuracy.

[SOURCE: ISO/IEC Guide 99:2007, 2.15]
3.17
metadata
information about a resource
[SOURCE: ISO 19115-1:2014, 4.10]
3.18
resolution

unit associated with the least significant digit of a coordinate

Note 1 to entry: Coordinate resolution may have linear or angular units depending on the characteristics of the

coordinate system.
3.19
sexagesimal degree
angle represented by a sequence of values in degrees, minutes, and seconds

Note 1 to entry: In the case of latitude or longitude, it may also include a character indicating hemisphere.

EXAMPLE 50.0795725 decimal degrees is represented as 50°04'46.461"
3.20
tuple
ordered list of values
Note 1 to entry: The number of values in a tuple is immutable.
[SOURCE: ISO 19136-1:2020, 3.1.60]
4 Abbreviated terms and character code notations
4.1 Abbreviated terms
CRS coordinate reference system
CRScsd coordinate reference system character string delimiter
EPSG EPSG geodetic parameter dataset
GML Geography Markup Language
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ISO 6709:2021(E)
HTML HyperText Markup Language
GPL geographic point location
ISOGR ISO Geodetic Registry
JSON JavaScript Object Notation
lat latitude
lon longitude
OGC Open Geospatial Consortium
UCS Universal Coded Character Set
URL Uniform Resource Locator
WKT well-known text
XML eXtensible Markup Language
4.2 Character code notations

Character string delimiters required in this document are represented in accordance with notation

from ISO/IEC 10646. Character names and code points are specified in Annex F, Table F.1.

5 Conformance

To conform to this document, representations of GPL shall satisfy the conditions specified in the

abstract test suite (Annex A).
6 Geographic point location (GPL) representation
6.1 Overview

This edition of ISO 6709 revises and expands the representation of geographic point location (GPL),

while maintaining an option (Annex B) for backwards compatibility with the previous edition

(ISO 6709:2008).

ISO 19111 defines the elements required to describe a CRS. A coordinate tuple represents a location

unambiguously only if the CRS to which it is referenced is identified, and if that CRS is dynamic the

epoch of the coordinates is also identified. Without this identification, uncertainty in position can result

in the location being as much as several hundred metres distant (see Annex C).

In this document, CRS identifiers shall accompany all GPL representations. Identification may be

through:
— a complete URL notation [6.5 a)],
— an abbreviated notation [6.5 b)] or
— a complete CRS definition as specified in ISO 19111, [6.5 c)].

ISO 19111 specifies several CRS types, of which the following are supported in this document. Any one,

or a combination of these, shall accompany all GPL representations:
— geodetic CRS — three-dimensional,
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— geographic CRS — two-dimensional or three-dimensional,
— projected CRS — two-dimensional, or sometimes three-dimensional,

— engineering CRS — two-dimensional, or sometimes one-dimensional or three-dimensional,

— parametric CRS — one-dimensional, with normally vertical orientation,
— vertical CRS — one-dimensional,
— temporal CRS — one-dimensional, and
— compound CRS.

NOTE For detailed information about each of these CRS types users can consult ISO 19111.

The text string representation format defined in 6.6 is used for single GPL instances. However, in

practice, GPL instances with uniform representation formats are commonly grouped into coordinate

sets that often provide a single CRS identification for the complete coordinate set. This single

identification does not adhere to the specified representation requirements defined by this document.

These types of coordinate sets are commonly formatted as files on digital storage, or structures in

computer memory.

This document does not specify the format of these coordinate sets, and when coordinate sets are used,

this document recommends that users provide suitable, clear and persistent documentation detailing

the CRS identifiers of all elements in the GPL representation, and character encoding used.

6.2 Component representation

This document specifies the representation of GPLs using the descriptive concept of a component. Each

component is comprised of three required elements:
— a coordinate tuple (6.3),
— a character string delimiter (6.4), and
— a CRS identifier (6.5).
A series of components can then be combined to define a GPL representation.

The order of the components occurring in a GPL representation text string is not defined by this

document and therefore enables any ordering of the components according to user or system

requirements, provided a valid CRS identifier element accompanies each component. Parsing and

identification of each component is possible by examining the character string delimiter.

The order and units of the coordinate tuples in each component are defined by the specific CRS.

However, in a compound CRS, the CRS not only defines the required coordinate tuples but also the order

of the components within the compound group.
6.3 Coordinate tuple

A coordinate tuple is an ordered list of values composed of coordinates. The coordinates within a

coordinate tuple are mutually independent. The number of coordinates in a tuple is equal to the

dimension of the coordinate system and the order of the coordinates in the coordinate tuple is identical

to the order of the axes of the coordinate system. The order and units of the coordinate tuple are

specified in the CRS definition associated with the component.
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6.4 Character string delimiters and terminator notation

To differentiate GPL strings specified in this document from those represented using formats defined

in the previous edition (ISO 6709:2008, Annex E.2), a new CRS character string delimiter (CRScsd) is

defined.

For specific formatting requirements shown in this document, users should refer to the character

encodings defined in Table F.1.

NOTE 1 Within this document, the notation CRScsd refers to a general CRS character string delimiter reference.

The format of the new CRScsd is composed of:
— the uppercase letters "CRS", immediately followed by;
— a single digit, either a 1, 2, 3 or 4, immediately followed by;
— a lowercase "d".
EXAMPLE 1 CRS2d is an example of a well-formed CRScsd.

The two characters immediately following the "CRS" together represent the dimension of the CRS, and

are referred to as the suffix of the CRS character string delimiter.
The following CRScsd strings represent the CRS types supported by this document:
a) CRS1d: one-dimensional spatial or temporal CRS.

EXAMPLE 2 Height, depth, pressure, and time are examples of one-dimensional coordinate tuple

elements.
b) CRS2d: two-dimensional single spatial CRS or two-dimensional compound CRS.

EXAMPLE 3 Lat/Lon, X/Y, Easting/Northing, and polar coordinates are examples of two-dimensional

coordinate tuple elements. A two-dimensional compound CRS identifier can define elements such as height

and time.

c) CRS3d: three-dimensional single spatial CRS or three-dimensional compound CRS.

EXAMPLE 4 Lat/Lon/height, X/Y/Z, and spherical coordinates are examples of three-dimensional

coordinate tuple elements. A three-dimensional compound CRS identifier can define elements such as

...