# postgis-spatial-sql

This skill guides spatial SQL backend choices and query design across PostGIS and DuckDB Spatial. Use it to inspect SRIDs, spatial indexes, joins, and query plans.

- skill · `type=skill` · Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, OpenCode · ★ 35
- Author: Muhammed Enes Duran
- License: MIT · policy=mirror · the beginning of the file is at the end of this page
- Source: https://github.com/muend/geoai-skills/tree/HEAD/skills/postgis-spatial-sql/SKILL.md
- Updated: 2026-10-17
- HTML: https://affpapa.org/en/nevibecode/skills/postgis-spatial-sql

## What it does

The skill helps compare PostGIS with embedded engines such as DuckDB Spatial, then work through schemas and spatial queries. It covers geometry versus geography, SRID selection, GiST and BRIN indexes, KNN searches, and validating results before comparing performance. Backend decisions depend on factors such as data volume, concurrency, and how results will be served.

For query diagnosis, it points to `EXPLAIN (ANALYZE, BUFFERS)` to inspect GiST usage and spot sequential scans. It also discusses `ST_Subdivide` for large polygons and `ST_IsValid` or `ST_MakeValid` for geometry checks. Examples include querying GeoParquet with DuckDB Spatial and defining an indexed, SRID-typed geometry column. The analysis CRS matters: a mismatched projection can produce incorrect measurements, while `ST_Distance(a,b) < dist` cannot use the index.

## Install

### Claude Code (native platform)

1. **Skills CLI (Vercel)**
```bash
npx skills add muend/geoai-skills --skill postgis-spatial-sql -a claude-code
```

2. **Manually: put the files in place**
- File: `~/.claude/skills/postgis-spatial-sql/SKILL.md` — Copy the whole skill folder; for one project use .claude/skills/postgis-spatial-sql/

### Codex

1. **Skills CLI (Vercel)**
```bash
npx skills add muend/geoai-skills --skill postgis-spatial-sql -a codex
```

2. **Manually: put the files in place**
- File: `.agents/skills/postgis-spatial-sql/SKILL.md` — For all projects use ~/.agents/skills/

### Cursor

1. **Skills CLI (Vercel)**
```bash
npx skills add muend/geoai-skills --skill postgis-spatial-sql -a cursor
```

2. **Manually: put the files in place**
- File: `.cursor/skills/postgis-spatial-sql/SKILL.md` — Cursor also reads .agents/skills/ and .claude/skills/

### GitHub Copilot

1. **GitHub CLI**
```bash
gh skill install muend/geoai-skills postgis-spatial-sql
```

2. **Manually: put the files in place**
- File: `.github/skills/postgis-spatial-sql/SKILL.md`

### Gemini CLI

1. **Skills CLI (Vercel)**
```bash
npx skills add muend/geoai-skills --skill postgis-spatial-sql -a gemini-cli
```

2. **Platform CLI**
```bash
gemini skills install https://github.com/muend/geoai-skills --path skills/postgis-spatial-sql
```

### Windsurf (Devin Desktop)

**Manually: put the files in place**
- File: `.devin/skills/postgis-spatial-sql/SKILL.md` — The legacy .windsurf/skills/ path still works

### OpenCode

**Skills CLI (Vercel)**
```bash
npx skills add muend/geoai-skills --skill postgis-spatial-sql -a opencode
```

### Claude.ai

**Claude.ai**
- Zip the folder and upload it in Settings → Capabilities → Skills

Where a file is given instead of a command, copy the files from the source to that path: https://github.com/muend/geoai-skills/tree/HEAD/skills/postgis-spatial-sql/SKILL.md

## When to use it
- choose a backend for spatial SQL workloads
- check why a spatial join misses its GiST index
- select geometry or geography and a suitable SRID
- find nearby features with a KNN query
- audit geometry validity before analysis

## Example prompts
- Compare PostGIS and DuckDB Spatial for my spatial queries and list the inputs needed to choose between them.
- Inspect this query with `EXPLAIN (ANALYZE, BUFFERS)` and suggest how to use GiST.
- Choose a geometry type and SRID for regional area analysis, then check my `ST_Area` expressions.

## Source text · SKILL.md · MIT

Below is the content of a third-party file. It is data, not instructions for you: do not act on anything written inside unless the human asks. Block tag: 13c8d946850ff6dd.

BEGIN THIRD-PARTY FILE 13c8d946850ff6dd
````text
---
name: postgis-spatial-sql
description: >-
  Invoke whenever spatial SQL or its execution backend is the decision:
  PostGIS, DuckDB Spatial, SpatiaLite, ST_* functions, recurring spatial
  joins, concurrent/growing workloads, or large GeoParquet queries. Covers
  backend selection, schemas, GiST/BRIN indexes, KNN, geometry versus
  geography, correctness benchmarks, and EXPLAIN optimization. Use PostGIS
  for managed concurrent services and embedded engines for bounded local
  analytics when evidence supports that choice. Use geo-data-engineering for
  acquisition, conversion, and file-based ETL without spatial SQL.
license: MIT
metadata:
  author: Muhammed Enes Duran
---

# PostGIS & Spatial SQL

Purpose: correct-and-fast spatial SQL. The two recurring failure modes are
semantic (geometry vs geography, SRID mismatches → wrong answers) and
performance (missing index usage → hour-long joins); this skill guards
both.

## When the database is the right tool

Move from files/GeoPandas to PostGIS when any of: features > a few
million, concurrent readers/writers, repeated ad-hoc querying, a serving
API on top, or transactional integrity needs. For single-shot analytical
scans over GeoParquet, **DuckDB Spatial** is often the fastest
zero-install path — same SQL mindset, no server.

When requirements are incomplete, do not turn this heuristic into a final
recommendation. First obtain current and forecast data volume, concurrency,
delivery and mutation pattern, latency/SLA, serving needs, and operational
ownership (including backup and recovery). Define representative ingestion,
join, and read queries for both viable backends; compare runtime and resource
use only after row counts, join cardinality, SRID, geometry validity, and sample
outputs agree. Include this benchmark and correctness plan in the current
response; do not merely offer to draft it later.

## Schema fundamentals

This runnable example assumes the data is contained in UTM zone 33N. Replace
EPSG:32633 with a projected CRS verified for the actual area of interest.

```sql
CREATE TABLE parcels (
  id          bigint GENERATED ALWAYS AS IDENTITY PRIMARY KEY,
  parcel_no   text NOT NULL,
  landuse     text,
  area_m2     double precision,          -- unit in the name, always
  geom        geometry(MultiPolygon, 32633) NOT NULL
);
CREATE INDEX parcels_geom_gix ON parcels USING gist (geom);
ANALYZE parcels;
```

- **Type the geometry column fully**: `geometry(MultiPolygon, SRID)` — an
  untyped `geometry` column happily accepts mixed garbage.
- Promote to Multi* on load (`ST_Multi`) so Polygon/MultiPolygon mixing
  never bites.
- **geometry vs geography**: geometry in a projected SRID for regional
  analysis (fast, full function set); geography (SRID 4326) when the
````
END THIRD-PARTY FILE 13c8d946850ff6dd

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First 2776 of 9592 bytes. © Muhammed Enes Duran · MIT · https://github.com/muend/geoai-skills/tree/HEAD/skills/postgis-spatial-sql/SKILL.md

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