GeoZarr SWG Monthly Meeting, 3 December 2025

Meeting Purpose

Align on GeoZarr's scope and define a path to a first release.

Key Takeaways

• New direction. GeoZarr will shift from a complex, abstract model (CDM) to a collection of simple, composable Zarr Conventions, directly addressing developer needs.
• First release. The GeoProj (CRS) and Multiscales conventions will be released as Release Candidates by Dec 15, providing immediate value.
• Leadership. Max Jones was approved as interim co-chair; a formal election for a new two-year term will occur in February.
• Process. PRs will now be reviewed asynchronously on GitHub to accelerate development, freeing up meetings for strategic discussion.

Topics

GeoZarr scope and strategy

• Problem. The current CDM-based approach is too complex and has prevented a first release. Developers need simple answers for basic geospatial metadata (CRS, projection, overviews).
• Solution. Adopt an incremental, feature-driven strategy.
  • Rationale: This delivers immediate value and builds momentum, avoiding the paralysis of trying to solve all problems at once.
  • Example roadmap: Release CRS, then Overviews, then Vertical Coordinates.
• New framework. The Zarr Conventions Framework provides the mechanism for this strategy.
  • Function: A standard way for communities (e.g., geospatial, bioimaging) to register and share their metadata conventions within Zarr.
  • Mechanism: A Zarr Conventions attribute in Zarr metadata points to a convention's spec URL, schema, or UUID.
  • Benefit: Allows for parallel development and sequential releases of conventions.

First release: GeoProj and Multiscales

• The first two conventions will be released as Release Candidates by Dec 15.
• GeoProj convention.
  • Purpose: Defines how to store CRS and projection information.
  • Rationale: Addresses the most urgent and frequently requested feature.
• Multiscales convention.
  • Purpose: A domain-agnostic convention for defining data overviews.
  • Rationale: Provides a generic resampling mechanism for analysis, which can be composed with domain-specific extensions like Tile Matrix Sets (TMS) for visualization.
  • Status: Considered mature enough for release after multiple review cycles.

Group leadership and process

• Chair elections.
  • The current two-year chair mandate ends in February.
  • Interim co-chair: Max Jones was approved as interim co-chair to fill a vacancy.
  • Formal election: A call for nominations will open in January for a new two-year term, with the election in February.
• PR review process.
  • Decision: PRs will now be reviewed and merged asynchronously on GitHub.
  • Rationale: This removes the synchronous meeting bottleneck, accelerating development. Meetings will focus on topics without consensus.

Next Steps / Action Items

• Max Jones
  • Announce the interim co-chair role to the OGC.
  • Send a calendar invite for co-working sessions (Mon/Wed/Fri at 9:30 AM PT).
  • Release the GeoProj and Multiscales conventions as Release Candidates by Dec 15.
• Christophe Noël
  • Draft a communication for OGC members on the new convention-based strategy.
• All
  • Engage in the GeoProj and Multiscales repositories to help finalize the Release Candidates.