generateLocationSteps.js

function toRad(deg) {
  return deg * (Math.PI / 180);
}
function toDeg(rad) {
  return rad / (Math.PI / 180);
}
const EARTH_R = 6378.1;

function getNewCoords(initLoc, distance, bearing) {
  const bearingR = toRad(bearing);
  const initCoords = {lat: toRad(initLoc.lat), lng: toRad(initLoc.lng)};
  const newLat = Math.asin(Math.sin(initCoords.lat) * Math.cos(distance/EARTH_R) +
    Math.cos(initCoords.lat) * Math.sin(distance/EARTH_R) * Math.cos(bearingR));
  const newLng = initCoords.lng + Math.atan2(Math.sin(bearingR) * Math.sin(distance/EARTH_R) *
    Math.cos(initCoords.lat), Math.cos(distance/EARTH_R) - Math.sin(initCoords.lat) * Math.sin(newLat));
  return {lat: toDeg(newLat), lng: toDeg(newLng)};
}

function generateLocationSteps(initialLocation, stepCount=12) {
  const NORTH = 0,
    EAST = 90,
    SOUTH = 180,
    WEST = 270;

  const pulseRadius = 0.07;               // km - radius of players heartbeat is 70m
  const xdist = Math.sqrt(3)*pulseRadius; // dist between column centers
  const ydist = 3*(pulseRadius/2);        // dist between row centers

  let locations = [initialLocation];

  let ring = 1;
  let loc = initialLocation;
  while (ring < stepCount) {
    loc = getNewCoords(loc, ydist, NORTH);
    loc = getNewCoords(loc, xdist/2, WEST);
    for (let direction=0; direction < 6; direction++) {
      for (let i=0; i < ring ; i++) {
        if (direction === 0) {  // RIGHT
          loc = getNewCoords(loc, xdist, EAST)
        }
        if (direction === 1) { // DOWN + RIGHT
          loc = getNewCoords(loc, ydist, SOUTH)
          loc = getNewCoords(loc, xdist/2, EAST)
        }
        if (direction === 2) { // DOWN + LEFT
          loc = getNewCoords(loc, ydist, SOUTH)
          loc = getNewCoords(loc, xdist/2, WEST)
        }
        if (direction === 3) { // LEFT
          loc = getNewCoords(loc, xdist, WEST)
        }
        if (direction === 4) { // UP + LEFT
          loc = getNewCoords(loc, ydist, NORTH)
          loc = getNewCoords(loc, xdist/2, WEST)
        }
        if (direction === 5) { // UP + RIGHT
          loc = getNewCoords(loc, ydist, NORTH)
          loc = getNewCoords(loc, xdist/2, EAST)
        }
        locations.push(loc);
      }
    }
    ring = ring + 1;
  }
  return locations;
}

example usage:

const coords = generateLocationSteps({lat: 1234, lng: 1234});