tile-grid-aggregation.js

var turf = require('turf')
var tilebelt = require('tilebelt')

// put your own data here
var stargazers = [<list of lat lons>]
// this sets the size of your grid cells; each grid cell is a map tile at the given zoom
var zoom = 12 
// tiles is a hash we can quickly add new tiles too and increment counts
var tiles = {}

stargazers.features.forEach(function(star){
  // star.lon and star.lat are placeholders. use the appropriate attributes for your data
  // our hash key for a tile is simply the tiles x, y, and z joined by a '/'; ie: "123/321/12"
  var tile = tilebelt.pointToTile(star.lon, star.lat, zoom).join('/')
  // if we have not seen the tile before, create a new key and set its value to 1
  if(!tiles[tile]) tiles[tile] = 1
  // if we have seen the tile before, increment the count by 1
  else tiles[tile]++ 
})

// our tiles hash contains counts for each tile, so now we can convert it to geojson http://geojson.org/
var fc = turf.featurecollection([])

// Object.keys returns an array of all the keys contained in the hash, and we can immediately loop over these using forEach
Object.keys(tiles).forEach(function(tile){
  // split the tile key into an array and map the items to numbers
  var poly = tilebelt.tileToGeoJSON(tile.split('/').map(Number))
  // grab the count for the associated tile and set it on the geojson property object
  poly.properties.stars = tiles[tile]
  //add the new polygon to our featurecollection
  fc.features.push(poly)
})

// print the result in stringified form
console.log(JSON.stringify(fc))

// try creating a choloropleth in geocolor or QGIS 
// - http://geocolor.io/  
// - http://qgis.org/en/site/
// - https://en.wikipedia.org/wiki/Choropleth_map
// choloropleth maps can be automated and created dynamically using the geocolor library https://github.com/morganherlocker/geocolor