Bounding Box Calculator

In short A bounding box is the rectangle of latitude and longitude that contains a circle of a given radius, and it exists because databases can index a box far faster than they can compute a distance. The arithmetic has one trap that catches almost everyone: a degree of latitude is about 111 km everywhere, but a degree of longitude shrinks from 111 km at the equator to nothing at the poles. Using the same degree offset for both — which is the most common implementation — produces a box that is far too narrow near the equator or absurdly wide near the poles. The offsets have to be computed separately, using the cosine of the latitude for longitude. Two more failures are worth naming because they are silent. A box that crosses the antimeridian has a western edge numerically GREATER than its eastern edge, which breaks any query written as west < longitude < east; such a box has to be split in two at ±180°, and most software does not do it automatically. And a box that reaches a pole covers every longitude, so it stops being a rectangle at all. Finally, remember that the box is not the circle: its corners lie about 41% further from the centre than the radius, so filtering by box alone returns points outside your radius. The standard approach is box first for speed, then true distance to trim.