/design-postgis-tables

name: design-postgis-tables
description: Comprehensive PostGIS spatial table design reference covering geometry types, coordinate systems, spatial indexing, and performance patterns for location-based applications
license: Apache-2.0
compatibility: Requires PostgreSQL 15+ with the PostGIS extension
metadata:
  author: tigerdata

PostGIS Spatial Table Design

Before You Start (5 Questions)

1. What is the geographic scope (single city/region vs global)? 2. What are your primary query patterns (within-radius, bbox, intersects, nearest-neighbor)? 3. What units do you need for distance/area (meters vs CRS units), and how accurate must they be? 4. What is the expected scale (rows, write rate), and is the data mostly append-only? 5. Do you need 3D (Z) or measures (M), or is 2D enough?

**SQL injection note:** When turning these patterns into application code, use parameterized queries for user-provided values (WKT/WKB, coordinates, IDs, radii). Avoid string-concatenating untrusted input into SQL; for dynamic identifiers, use safe identifier quoting/whitelisting.

Core Rules

• **Always use PostGIS geometry/geography types** instead of PostgreSQL's built-in geometric types (`POINT`, `LINE`, `POLYGON`, `CIRCLE`). PostGIS types provide true spatial capabilities.
• **Choose between GEOMETRY and GEOGRAPHY** based on your use case: GEOMETRY for projected/local data with Cartesian math; GEOGRAPHY for global data requiring accurate spherical calculations.
• **Always specify SRID** (Spatial Reference Identifier) when creating geometry columns. Use `4326` (WGS84) for GPS/global data, appropriate local projections for regional data.
• **Create spatial indexes** on all geometry/geography columns using GiST (default). Consider BRIN only for very large **GEOMETRY** tables where rows are naturally ordered on disk and you can tolerate coarser filtering.
• **Use constraint-based type enforcement** with `GEOMETRY(type, SRID)` syntax to ensure data integrity.

Geometry vs Geography

When to Use GEOMETRY

• **Local/regional data** within a single coordinate system
• **Projected coordinates** (meters, feet) for accurate area/distance calculations
• **Complex spatial operations** (buffering, unions, intersections)
• **Performance-critical queries** (Cartesian math is faster)
• **Data already in a projected CRS** (UTM, State Plane, etc.)

-- Regional data with projected coordinates (UTM Zone 10N for California)
CREATE TABLE local_parcels (
    id BIGINT GENERATED ALWAYS AS IDENTITY PRIMARY KEY,
    parcel_number TEXT NOT NULL,
    boundary GEOMETRY(POLYGON, 26910),  -- UTM Zone 10N (meters)
    area_sqm DOUBLE PRECISION GENERATED ALWAYS AS (ST_Area(boundary)) STORED
);

When to Use GEOGRAPHY

• **Global data** spanning multiple continents/hemispheres
• **GPS coordinates** (latitude/longitude in decimal degrees)
• **Accurate distance calculations** on Earth's surface (great circle)
• **Simple spatial operations** (distance, containment)
• **Data from GPS devices, geocoding services, or web maps**

-- Global data with geodetic calculations
CREATE TABLE global_offices (
    id BIGINT GENERATED ALWAYS AS IDENTITY PRIMARY KEY,
    name TEXT NOT NULL,
    city TEXT NOT NULL,
    location GEOGRAPHY(POINT, 4326)  -- WGS84 (lat/lon)
);

-- Distance in meters (accurate spherical calculation)
SELECT
    a.name AS office_a,
    b.name AS office_b,
    ST_Distance(a.location, b.location) / 1000 AS distance_km
FROM global_offices a
CROSS JOIN global_offices b
WHERE a.id < b.id;

Comparison Table

| Aspect | GEOMETRY | GEOGRAPHY | | ----------------- | ------------------------------------- | ------------------------- | | Coordinate system | Any SRID (projected or geodetic) | WGS84 (SRID 4326) only | | Distance units | CRS units (degrees, meters, feet) | Meters (always) | | Distance accuracy | Depends on projection | True spheroidal distance | | Area accuracy | Accurate in projected CRS | Accurate on sphere | | Function support | Full (300+ functions) | Limited (~40 functions) | | Performance | Faster (Cartesian math) | Slower (spherical math) | | Index type | GiST, BRIN, SP-GiST | GiST only | | Best for | Regional/local data, complex analysis | Global data, GPS tracking |

Geometry Types

Point Types

-- Single location (stores, sensors, events)
location GEOMETRY(POINT, 4326)

-- Multiple discrete locations (multi-branch business)
locations GEOMETRY(MULTIPOINT, 4326)

-- 3D point with elevation
location_3d GEOMETRY(POINTZ, 4326)

-- Point with measure value (linear referencing)
location_m GEOMETRY(POINTM, 4326)

**Use POINT for:** Store locations, sensor positions, event coordinates, addresses, POIs **Use MULTIPOINT for:** Multiple related locations stored as single feature

Line Types

-- Single path (road segment, river, route)
path GEOMETRY(LINESTRING, 4326)

-- Multiple paths (road network, transit lines)
network GEOMETRY(MULTILINESTRING, 4326)

-- 3D line with elevation profile
trail_3d GEOMETRY(LINESTRINGZ, 4326)

**Use LINESTRING for:** Roads, rivers, pipelines, GPS tracks, routes **Use MULTILINESTRING for:** Disconnected road segments, river systems

Polygon Types

-- Single area (parcel, building footprint, zone)
boundary GEOMETRY(POLYGON, 4326)

-- Multiple areas (archipelago, fragmented habitat)
territories GEOMETRY(MULTIPOLYGON, 4326)

-- 3D polygon (building with height)
footprint_3d GEOMETRY(POLYGONZ, 4326)

**Use POLYGON for:** Property boundaries, administrative areas, service zones **Use MULTIPOLYGON for:** Countries with islands, fragmented regions

Generic Types

-- Any geometry type (flexible schema)
geom GEOMETRY(GEOMETRY, 4326)

-- Collection of mixed types
features GEOMETRY(GEOMETRYCOLLECTI