# Geospatial Patterns

Store locations and query by radius, distance, or bounding box using GEOADD, GEOSEARCH, and GEODIST commands built on geohash-encoded Sorted Sets.

Redis natively supports geospatial indexes using the GEO* command family. Coordinates are stored as geohashes in a Sorted Set, enabling efficient spatial queries for "find nearby" features.

## Adding Locations

Store locations with their coordinates (longitude first, then latitude):

    GEOADD locations -122.4194 37.7749 "san_francisco"
    GEOADD locations -73.9857 40.7484 "new_york"
    GEOADD locations -0.1276 51.5074 "london"

Multiple locations can be added in a single command:

    GEOADD locations -122.4194 37.7749 "san_francisco" -73.9857 40.7484 "new_york"

## Retrieving Coordinates

Get the coordinates of stored locations:

    GEOPOS locations "san_francisco"

Returns the longitude and latitude as a nested array.

## Calculating Distance

Measure distance between two members:

    GEODIST locations "san_francisco" "new_york" km

Supported units: `m` (meters), `km` (kilometers), `mi` (miles), `ft` (feet).

## Searching by Radius

Find all locations within a specified radius:

    GEOSEARCH locations FROMMEMBER "san_francisco" BYRADIUS 500 km

Search from specific coordinates:

    GEOSEARCH locations FROMLONLAT -122.4 37.8 BYRADIUS 50 km

## Search Options

GEOSEARCH supports several options for controlling output:

    GEOSEARCH locations FROMLONLAT -122.4 37.8 BYRADIUS 50 km WITHCOORD WITHDIST COUNT 10 ASC

- `WITHCOORD`: Include coordinates in results
- `WITHDIST`: Include distance from search point
- `WITHHASH`: Include the geohash integer
- `COUNT N`: Limit results to N items
- `ASC/DESC`: Sort by distance (ascending = closest first)

## Searching by Bounding Box

Search within a rectangular area:

    GEOSEARCH locations FROMMEMBER "san_francisco" BYBOX 1000 1000 km

The box is specified as width × height centered on the reference point.

## Storing Search Results

Save search results to a new key for further processing:

    GEOSEARCHSTORE nearby_cache locations FROMLONLAT -122.4 37.8 BYRADIUS 50 km

The results are stored as a Sorted Set with geohash scores.

## Location with Metadata

Since GEO commands use Sorted Sets, you can only store the member name directly. Store additional metadata in a separate Hash:

    GEOADD restaurants -122.4194 37.7749 "restaurant:123"
    HSET restaurant:123 name "Joe's Diner" cuisine "American" rating "4.5"

When searching, first find nearby IDs, then fetch their metadata:

    GEOSEARCH restaurants FROMLONLAT -122.4 37.8 BYRADIUS 5 km
    HGETALL restaurant:123

## Real-Time Location Tracking

For tracking moving entities like drivers or delivery personnel:

1. Update location on each GPS ping:

       GEOADD drivers -122.4 37.8 "driver:456"

2. Store last-update timestamp:

       HSET driver:456:status last_update 1706648400 available 1

3. Find nearby available drivers:

       GEOSEARCH drivers FROMLONLAT -122.4 37.8 BYRADIUS 5 km COUNT 20

4. Filter results by checking availability and freshness in your application.

## Geofencing

Geofencing detects when entities enter or leave defined areas. Redis doesn't provide built-in geofencing events, but you can implement it by:

1. Storing geofence definitions (center coordinates and radius)
2. On each location update, checking if the entity is inside each relevant fence
3. Comparing current state to previous state to detect enter/exit events
4. Using Pub/Sub to broadcast geofence events to interested services

## Geohash

Get the geohash string representation:

    GEOHASH locations "san_francisco"

Geohashes are useful for:
- Debugging and visualization
- Interoperability with other geospatial systems
- Understanding the precision of stored coordinates

## Removing Locations

Since GEO data is stored in a Sorted Set, use ZREM:

    ZREM locations "san_francisco"

## Commands Reference

| Command | Description |
|---------|-------------|
| GEOADD | Add coordinates for members |
| GEOPOS | Get coordinates of members |
| GEODIST | Distance between two members |
| GEOSEARCH | Search by radius or box |
| GEOSEARCHSTORE | Search and store results |
| GEOHASH | Get geohash strings |
| ZREM | Remove a location |