ISO 19162:2019

Overview

ISO 19162:2019 - Geographic information - Well-known text representation of coordinate reference systems (WKT) defines a concise, text-string format for representing coordinate reference systems (CRSs) and commonly needed coordinate operations. The WKT string is designed to be machine- and human-readable, preserving simplicity and interoperability with the abstract CRS model described in ISO 19111. The standard intentionally constrains some expressive elements of ISO 19111 (for example, it excludes parameter grouping and pass-through operations) to keep WKT compact and unambiguous. Note: a WKT string is not intended as a full storage format because it omits metadata about data source and applicability.

Key technical topics and requirements

• Structure and syntax: formal grammar (Backus‑Naur Form) and rules that define WKT token order and nesting.
• Encoding and characters: allowed characters, numeric formats, date/time elements, double-quote handling and delimiter rules.
• Case sensitivity and reserved keywords: which tokens are fixed and how implementations must treat names and identifiers.
• Conformance: requirements for compliant WKT producers and parsers to ensure interoperability.
• Common attribute representation: standardized WKT forms for name, scope, extent, identifier, remark, units and conversion factors.
• Coordinate systems and axes: syntax for coordinate system types, dimensionality, axis names, directions, units and axis order.
• Datums and geodetic elements: representation of ellipsoids, prime meridians and geodetic reference frames.
• CRS classes: explicit WKT forms for geodetic/geographic, projected, vertical, engineering, parametric, temporal and derived CRSs.
• Map projections and parameters: representation of projection methods, parameters and identifiers while keeping math referenced rather than embedded.
• Backward compatibility: guidance to handle legacy WKT variants and migration strategies.
• Examples: illustrative WKT strings for typical CRSs and derived CRSs.

Practical applications and users

ISO 19162 WKT is used where compact, interoperable CRS definitions are required:

• GIS software vendors and developers integrating coordinate reference systems and transformations.
• Spatial database engines and data exchange formats that embed CRS metadata in a readable string.
• Cartographers, surveyors and geospatial analysts who need unambiguous CRS descriptions for data composition, reprojection and visualization.
• Geospatial standards bodies and implementers aligning systems to ISO models (ISO 19111).

Benefits include improved interoperability, easier manual inspection of CRS definitions, and standardized parsing across tools - while relying on external references for complex coordinate operation mathematics.

Related standards

• ISO 19111 - Abstract model for coordinate reference systems (referenced by ISO 19162 for the conceptual model and semantics).