Why PostGIS sets a max value for SRID IDs?

[Regina Obe]

I vaguely recall someone complaining about this 15 years ago, but not since then.

 

Paul can better speak for the reason, but I think it was because we needed to fit it into the header of the geometry and still have enough bits left for the geometry type etc and 2 bits extra for growth.

 

So I would say it’s very unlikely we’d lift this restriction.

 

From: G. Allegri <giohappy at gmail.com> 
Sent: Monday, October 27, 2025 5:46 AM
To: postgis-users at lists.osgeo.org
Subject: Why PostGIS sets a max value for SRID IDs?

 

Hello list,

 

I'm working on two projects where custom CRSs, with custom authorities and IDs are provided.

Both projects use IDs with numbers beyond SRID_USR_MAX=998999 [1], which is hardcoded in PostGIS for the spatial_ref_sys id field values.

I can use the auth_id, of course, but having to reassign an id < 998999 is a bit problematic for two reasons:

 

- I have custom transformation pipelines defined inside the proj.db, where the custom IDs are defined for CRSs. 

- other softwares (QGIS, Geoserver) can use the custom IDs but they cannot match the geometries SRIDs returned PostGIS

 

I wonder if there's a technical reason for the SRID_USR_MAX constant, and if there's any change to remove it in the future.

And I wonder if others have faced the problems I'm having due to this, and what are the solutions they came up with.

 

Thanks,

Giovanni

 

[1] https://github.com/postgis/postgis/blob/5dc95f1bc3047b048128616d4543b603b8bbdca7/configure.ac#L1554

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