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This repository contains the specification for the SOZip (Seek-Optimized Zip) profile to the ZIP file format.


What is SOZip ?

A Seek-Optimized ZIP file (SOZip) is a ZIP file that contains one or several Deflate-compressed files that are organized and annotated such that a SOZip-aware reader can perform very fast random access (seek) within a compressed file.

SOZip makes it possible to access large compressed files directly from a .zip file without prior decompression. It is not a new file format, but a profile of the existing ZIP format, done in a fully backward compatible way. ZIP readers that are non-SOZip aware can read a SOZip-enabled file normally and ignore the extended features that support efficient seek capability.

Software implementations

  • GDAL: C/C++ open source geospatial library. Try out its sozip branch, pending future inclusion in its master branch.
  • Python sozipfile module: drop-in replacement for standard zipfile module, creating SOZip-enabled files.

See Annex A: Software implementations for more details.

Examples of SOZip files

Examples of SOZip-enabled files can be found in the sozip-examples repository.

Other ZIP related specification

This GitHub organization also hosts the KeyValuePairs extra-field specification, to be able to encode arbitrary key-value pairs of metadata associated with a file within a ZIP. For example to store the Content-Type of a file.


Done with GDAL sozip branch, on a laptop running a Intel(R) Core(TM) i7-10750H CPU @ 2.60GHz (6 cores / 12 virtual CPUs).

  • ZIP generation:
Timing Action
6.1 s Multithreaded (12 vCPUs) generation of 489 MB SOZip-enabled file from a 1.6 GB uncompresssed GeoPackage file with
sozip nz-building-outlines.gpkg
36 s Single threaded compression of same file to 480 MB with regular zip utility with
zip nz-building-outlines.gpkg
  • Bulk reading: Multithreaded extraction (4 vCPUs) of 3.2 million features with Arrow Array interface
Timing Action
1.2 s from SOZip-compressed GeoPackage file with
0.7 s from uncompressed GeoPackage file with
bench_ogr_batch nz-building-outlines.gpkg
  • Subsetting: Extraction of 66,377 features with a spatial filter
Timing Action
1.2 s from SOZip-compressed GeoPackage file with
ogr2ogr out.gpkg -spat 1740000 5910000 1750000 5920000
1.1 s from uncompressed GeoPackage file with
ogr2ogr out.gpkg nz-building-outlines.gpkg -spat 1740000 5910000 1750000 5920000
  • Extraction of one feature from its identifier:
Timing Action
45 ms from SOZip-compressed GeoPackage file with
ogr2ogr out.gpkg -fid 1000000
44 ms from uncompressed GeoPackage file with
ogr2ogr out.gpkg nz-building-outlines.gpkg -fid 1000000

How to contribute ?

We welcome contributions to this specification as issues, pull requests or discussions.

If you use SOZip or plan to use it for your data delivery, or consider doing a SOZip implementation, etc., let us know!

Social media

Find me on Twitter and Mastodon


The SOZip specification and its GDAL implementation have been developed by Spatialys, with support from Safe Software