Best practices for documenting spatial reference systems, projections, and georeferencing decisions for geodata
Clear, durable documentation of spatial references, projections, and georeferencing decisions strengthens data reuse, interoperability, and reproducibility across disciplines, scales, and diverse software environments.
In geospatial work, every dataset carries an implicit commitment to accuracy and reproducibility through its spatial reference system, projection method, and the choices that anchored its geographic positioning. Documentation should begin with a concise description of the coordinate reference system, including its name, official code (for example EPSG), and the version of the standard used. It should also specify any local or regional adaptations, such as custom false eastings, modified datum shifts, or adjustments for coastal boundaries. Clear notes about when and why these decisions were made help future users understand the dataset’s spatial lineage and enable faithful reprojection if needed.
To support long-term clarity, maintain a single authoritative metadata section that records the rationale behind selecting a particular projection or CRS. This section should include the intended analysis scale, the geographic extent, and any aesthetic or technical constraints that influenced the choice, such as minimize distortion in a study area or preserve area for land management tasks. Include alternative options considered and the reasons they were rejected. The goal is to capture practical tradeoffs rather than hidden preferences, so that future researchers can assess suitability for new questions or different landscapes.
Spatial references should be described with reproducible detail
Beyond listing the CRS code, provide context about the dataset’s origin and intended use. Describe the coordinate system’s compatibility with widely used software packages and data standards, and note any known limitations or quirks encountered during data collection or processing. If the data were transformed, document the sequence of steps, including intermediate projections, resampling methods, and interpolation choices. This level of detail ensures that analysts can reproduce the transformation chain and evaluate results with confidence, rather than treating the dataset as a static snapshot.
Include a clear statement on the temporal validity of spatial references, especially for datasets integrated across time periods. If a projection or datum update occurred, describe how it was detected, who performed it, and what tests confirmed that the alignment remained consistent with the intended geographic frame. Provide guidance on how to handle historical versus current records, and outline any plans for reprocessing or revalidating data as standards evolve. Such forward-facing notes reduce surprises when new tools appear or when collaborators attempt to combine multiple datasets.
Validation and testing should accompany documentation
Reproducibility hinges on sharing exact parameters that define the geospatial frame. Record the projection name, code, datum, ellipsoid, units, and any grid or zone designations used during data creation. When relevant, include transformation parameters like Bursa-Wolfe or Helmert shifts and their source versions. Also document the software environments in which these parameters were derived, including versions of GIS platforms and any custom scripts. This precise accounting makes it feasible for others to replicate the coordinate frame, reproject data, and compare results across studies.
Where practical, attach machine-readable metadata files alongside human-readable descriptions. Encapsulate CRS definitions in standardized formats such as WKT or PROJ strings, and ensure encoding supports non-Latin scripts when datasets span multiple regions. A machine-readable record accelerates automated workflows, reduces the chance of misinterpretation, and enables seamless integration with catalog services, data portals, and archival repositories. Developers should also provide an easy path to verify the CRS by performing a basic transformation and comparing key control points before and after reprojection.
Future-proofing through standards and governance
Thorough validation checks are essential to trust geospatial references. Include examples that verify alignment against control points, crosswalks with known basemaps, or comparisons with alternative projections in the study area. Document the thresholds used for accepting discrepancies, whether they relate to distance errors, angular deviations, or area distortion. When possible, share the validation datasets and scripts used to run these checks, so auditors or collaborators independent of the original project can reproduce outcomes. Validation records should be time-stamped and linked to the specific dataset version they accompany.
Involve stakeholders from data producers, analysts, and data curators in the validation process. Collaborative reviews help surface edge cases, such as coastal distortions, curved boundaries, or irregularly shaped study areas where standard projections perform poorly. Feedback should be integrated into the metadata and, when necessary, into data processing pipelines. Maintaining an open log of validation occasions supports continual improvement and demonstrates accountability to both funders and users who rely on the geodata for decision making.
Practical guidance for diverse geospatial communities
Best practices emphasize adherence to established standards and open formats to maximize longevity. Use widely adopted CRS identifiers, keep up with updates from the EPSG dataset, and align with evolving geospatial metadata schemas. Governance around CRS selection should be transparent, with roles defined for data producers, stewards, and auditors. When datasets migrate between platforms, ensure that the CRS and all transformation steps remain traceable. Documentation should also address licensing and access restrictions for any reference data used to derive coordinate frames, guarding against inadvertent reuse constraints.
Plan for change management by recording how decisions would be revisited as standards shift. Provide a clear mapping from legacy CRSs to current equivalents, including reprojection strategies and risk assessments. Include timelines for revalidation and guidance on when to archive obsolete frames. Writing these forward-looking notes reduces the burden on future teams and supports the sustainable stewardship of geodata across decades, enabling consistent spatial reasoning even as technologies evolve.
For interdisciplinary teams, maintain uniform documentation templates that accommodate varied expertise levels. Use plain-language explanations for non-specialists while preserving the technical precision required by GIS professionals. Encourage the inclusion of pictorial representations of coordinate frames when possible, such as schematic diagrams showing the relationship between the dataset’s native CRS and its projected form. Clear cross-references to related datasets, basemaps, and analysis workflows help collaborators understand how the geodata fits within broader research or decision-making efforts.
Finally, cultivate a culture that treats geospatial metadata as an active, updateable resource rather than a one-time appendix. Schedule periodic reviews, solicit practical feedback, and archive historical versions with timestamped notes. By embedding CRS documentation in routine data management practices, organizations improve the reliability of analyses, enable seamless collaboration, and support trustworthy, reproducible science that remains accessible to users far beyond the original project timeframe.
