Bounding Box Finder

What a bounding box is for

A bounding box is the smallest axis-aligned rectangle containing your data. It is the cheapest possible spatial index: a database can reject millions of irrelevant rows by comparing four numbers before ever touching real geometry. In day-to-day work you need one for setting a map view, requesting a WMS or tile extract, restricting an Overpass query to a city, or clipping a national dataset down to a study area.

The ordering problem

Every ecosystem picked a different order for the same four numbers, which is why this tool prints all of them. GeoJSON and WMS 1.1 use minLng, minLat, maxLng, maxLat. Leaflet wants pairs of latitude then longitude, south-west corner first. Overpass and several OSM tools want south, west, north, east. Getting this wrong does not error — it silently queries the wrong part of the planet, which is much harder to notice.

• GeoJSON / WMS 1.1: minLng, minLat, maxLng, maxLat
• Leaflet: [[minLat, minLng], [maxLat, maxLng]]
• Overpass: south, west, north, east
• WMS 1.3 with EPSG:4326: axis order flips to lat first

Antimeridian and single-point files

Two cases deserve a warning. A dataset spanning the 180th meridian — Fiji, the Bering Sea, some Pacific shipping routes — produces a box that appears to wrap the whole globe, because a simple min/max cannot express the wrap. And a file containing one point produces a zero-width box; use the centre point and a fixed zoom rather than fitting bounds, or the map will zoom to maximum.

Using the extent to speed things up

Once you have the box, it is the fastest way to shrink a workload. Pass it to ogr2ogr with -clipsrc to cut a country file down to a district, use it as the bbox parameter on a tile or WMS request instead of downloading a full layer, or store it alongside each dataset so your application can decide what to load before parsing any geometry at all.