minimal image is too big (5.43GB) — investigation and potential improvements

[Robinlovelace]

Problem

The minimal image is currently 5.43GB, which is only slightly smaller than:

• latest (5.70GB)
• osgeo (6.07GB)
• suggests (5.67GB)

This undermines its purpose as a lightweight alternative. By comparison:

• python is 2.32GB
• pythonr is 4.37GB

Potential next steps

1. Audit the minimal Dockerfile to identify unnecessary layers, duplicate packages, or base-image bloat inherited from rocker/geospatial.
2. Compare with python (2.32GB) to see what Python-enabled images are doing differently to stay small.
3. Investigate whether rocker/geospatial itself is larger than necessary and whether we can:
   • Use a smaller base image (e.g., Debian slim or Ubuntu minimal).
   • Prune existing layers in the base image or use multi-stage builds.
4. Leverage rocker-versioned2 build scripts to let users mix and match components (R, Python, QGIS, etc.) rather than shipping a monolithic minimal image. Example reference: https://github.com/rocker-org/rocker-versioned2/blob/master/scripts/install_rstudio.sh
5. Document how advanced users can replicate the minimal setup using the rocker-versioned2 scripts and a smaller base image of their choice.

Proposed short-term fix

Open a PR with a reduced minimal image that removes non-essential packages and explores smaller base-image options, while keeping the geospatial stack functional.

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/cc @Robinlovelace @deargle