Building Geofences with Bounding Box Calculations

What is a Bounding Box?

A bounding box is a rectangle defined by two coordinate pairs: southwest corner (min_lat, min_lng) and northeast corner (max_lat, max_lng). Any point whose latitude and longitude fall within this rectangle is "inside the fence."

Bounding boxes are a lightweight alternative to polygon geofences. They're fast to compute, easy to index, and sufficient for most use cases where a rough boundary is acceptable.

Calculating a Bounding Box

Given a centre point and a radius, the API computes the bounding box:

curl -X POST https://api.toolkitapi.io/v1/geo/bounding-box \
  -H "X-API-Key: $API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "lat": 51.5074,
    "lng": -0.1278,
    "radius_km": 10
  }'

{
  "center": { "lat": 51.5074, "lng": -0.1278 },
  "radius_km": 10,
  "bbox": {
    "min_lat": 51.4175,
    "max_lat": 51.5973,
    "min_lng": -0.2737,
    "max_lng": 0.0181
  }
}

Database Indexing for Fast Lookups

Store latitude and longitude as indexed columns. A bounding box query becomes a simple range filter:

SELECT * FROM locations
WHERE lat BETWEEN :min_lat AND :max_lat
  AND lng BETWEEN :min_lng AND :max_lng;

Pair this with a post-filter using the Haversine formula to discard corner points outside the true circular radius.

When Bounding Boxes Are Enough

• Delivery radius checks (is this address within our service area?)
• Proximity search (find stores near me)
• Map tile selection

When to Use Polygons Instead

Complex geofences (country boundaries, irregular service zones, exclusion areas) require polygon containment tests. For those cases, use the GeoJSON polygon endpoint or a proper GIS stack.