[SPARK-56454][DOCS][FOLLOWUP] Document supported SRIDs in geospatial types

docs/sql-ref-geospatial-types.md

@@ -143,6 +143,65 @@ SELECT ST_Srid(ST_SetSrid(ST_GeomFromWKB(X'0101000000000000000000F03F00000000000
 * **Mixed-SRID columns** (`GEOMETRY(ANY)` or `GEOGRAPHY(ANY)`): Values can have different SRIDs. Only valid SRIDs are allowed.
 * **Storage**: Parquet, Delta, and Iceberg store geometry/geography with a fixed SRID per column; mixed-SRID types are for in-memory/query use. When writing to these formats, a concrete (fixed) SRID is required.
 
+### Supported SRIDs
+
+Spark includes a pre-built SRID registry that combines coordinate systems from the PROJ database with OGC standard overrides. This registry enables validation and proper handling of coordinate systems for geospatial data.
+
+**SRID Compatibility Rules:**
+- **GEOMETRY** accepts all SRIDs in the registry (geographic + projected + SRID 0)
+- **GEOGRAPHY** only accepts geographic SRIDs (latitude/longitude coordinate systems)
+
+#### PROJ Version by Spark Release
+
+| Spark Version | PROJ Version |
+|---------------|--------------|
+| 4.2.0 | 9.7.1 |
+
+The SRID registry is pinned to the PROJ version shown above and is not synced live with external databases.
+
+#### OGC Standard Overrides
+
+Spark applies the following OGC standard overrides to specific SRIDs from the PROJ database:
+
+| SRID | PROJ CRS Identifier | OGC CRS Identifier | Description |
+|------|---------------------|-------------------|-------------|
+| 4326 | `EPSG:4326` | `OGC:CRS84` | WGS 84 (longitude/latitude order per OGC standard) |
+| 4267 | `EPSG:4267` | `OGC:CRS27` | NAD27 |
+| 4269 | `EPSG:4269` | `OGC:CRS83` | NAD83 |
+
+
+#### Commonly Used SRIDs
+
+| SRID | CRS Identifier | Name | CRS Type | Description |
+|------|----------------|------|----------|-------------|
+| 0 | `SRID:0` | Unspecified | Cartesian | Coordinates with no defined CRS (default for `ST_GeomFromWKB(wkb)`) |
+| 4326 | `OGC:CRS84` | WGS 84 | Geographic | World Geodetic System 1984 (longitude/latitude), GPS coordinates, global data (default for GEOGRAPHY) |
+| 4267 | `OGC:CRS27` | NAD27 | Geographic | North American Datum 1927 |
+| 4269 | `OGC:CRS83` | NAD83 | Geographic | North American Datum 1983 |
+| 3857 | `EPSG:3857` | Web Mercator | Projected | Pseudo-Mercator projection used by web mapping services |
+
+**Notes:**
+* `GEOMETRY(0)` means a fixed SRID of 0. For mixed per-row SRIDs, use `GEOMETRY(ANY)`.
+* [Parquet](https://github.com/apache/parquet-format/blob/master/Geospatial.md)
+  and [Iceberg](https://github.com/apache/iceberg/blob/main/format/spec.md) geospatial
+  specifications require a fixed SRID per column, so they do not support persisting
+  `GEOMETRY(ANY)` or `GEOGRAPHY(ANY)`.
+
+#### SRID Validation
+
+**Invalid SRID (not in registry):**
+```sql
+SELECT ST_GeomFromWKB(X'0101000000000000000000F03F0000000000000040', 99999);
+-- Throws [ST_INVALID_SRID_VALUE]
+```
+
+**Projected SRID with GEOGRAPHY type:**
+```sql
+CREATE TABLE invalid_geo (id BIGINT, loc GEOGRAPHY(3857));
+-- Throws [ST_INVALID_SRID_VALUE] (3857 is projected, not geographic)
+```
+
+
 ### Data Types Reference
 
 For the full list of supported data types and API usage in Scala, Java, Python, and SQL, see [Data Types](sql-ref-datatypes.html).