geojson-points

Original：🇺🇸 English

Translated

Convert JSON rows with latitude/longitude fields into a GeoJSON FeatureCollection using raw PostGIS SQL.

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Sourcemmbmf1/geospatial-skills

Added on2026-02-10

NPX Install

npx skill4agent add mmbmf1/geospatial-skills geojson-points

SKILL.md Content

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Points → GeoJSON (PostGIS)

Use this skill when you have tabular data (rows or JSON) that include latitude/longitude fields and you need a GeoJSON

FeatureCollection

for map display.

This skill documents the canonical raw SQL pattern for building GeoJSON from point data in PostGIS.

When to use

You have rows like
```
{ id, lat, lng, ... }
```
You want GeoJSON directly from Postgres
You want predictable geometry and property handling

Input assumptions

Latitude and longitude are stored as numeric or castable to numeric
Longitude comes first in point construction
Geometry is output in WGS84 (EPSG:4326)

Canonical SQL pattern

From JSON input

Use when your API passes rows as a JSON array.

WITH data_rows AS (
  SELECT jsonb_array_elements($1::jsonb) AS row_data
)
SELECT jsonb_build_object(
  'type', 'FeatureCollection',
  'features', jsonb_agg(
    jsonb_build_object(
      'type', 'Feature',
      'geometry', ST_AsGeoJSON(
        ST_Point(
          (row_data->>'lng')::float,
          (row_data->>'lat')::float
        )
      )::jsonb,
      'properties', row_data - 'lat' - 'lng'
    )
  )
)
FROM data_rows;

From a table

Use when latitude/longitude are stored in columns.

SELECT jsonb_build_object(
  'type', 'FeatureCollection',
  'features', jsonb_agg(
    jsonb_build_object(
      'type', 'Feature',
      'geometry', ST_AsGeoJSON(
        ST_Point(lng, lat)
      )::jsonb,
      'properties', to_jsonb(t) - 'lat' - 'lng'
    )
  )
)
FROM my_table t;

Coordinate rules (critical)

GeoJSON coordinates are [longitude, latitude]
Latitude range:
```
-90..90
```
Longitude range:
```
-180..180
```

Most incorrect maps come from swapped coordinates.

Output shape

```
type
```
:
```
"FeatureCollection"
```
```
features
```
: array of GeoJSON
```
Feature
```
objects

Each feature has:

```
geometry.type = "Point"
```
```
geometry.coordinates = [lng, lat]
```
```
properties
```
= remaining fields

Implementation notes

Use

ST_Point(lng, lat)

(not

ST_MakePoint(lat, lng)

)

```
ST_AsGeoJSON(... )::jsonb
```
avoids string parsing downstream
Removing coord fields keeps
```
properties
```
clean and map-safe

Guardrails

Filter rows with missing or invalid coordinates before conversion
Enforce feature limits for browser safety
Explicitly select properties if payload size matters