These functions are for to generate points uniformly, randomly, and independently within a circle of radius r around a location (x0, y0),

latAndlonGenerator.js

/*These functions are for to generate points uniformly, randomly, and independently
within a circle of radius r around a location (x0, y0),
*/
function latAndlonGenerator (radius) {
const RADIUS_IN_METERS = 70000
  let r = RADIUS_IN_METERS / 111300,  // Convert meters in degrees (111,300 meters = a degree.)
    y0 = 40.416775,                  // Central point where to generate more coordinates, inside a circle
    x0 = -3.70379,                  // In this case, Madrid.
    u = Math.random(),
    v = Math.random(),
    w = r * Math.sqrt(u),
    t = 2 * Math.PI * v,
    x = w * Math.cos(t),
    y1 = w * Math.sin(t),
    x1 = x / Math.cos(y0)

  newY = y0 + y1
  newX = x0 + x1

  return {lat: newY, lon: newX}
}