Styling Leaflet circleMarkers by numerical property with a color ramp

Synthetic GeoJSON data are created with a quasi-normal spatial distribution and displayed as circle markers on a Leaflet map. The markers are styled using a color ramp that is tied to a numerical property ("year" in this case).

by benjrei

HTML

<link rel="stylesheet" href="http://cdn.leafletjs.com/leaflet-0.7.2/leaflet.css">
<script src="http://cdn.leafletjs.com/leaflet-0.7.2/leaflet.js"></script>
<div id="map"></div>

CSS

html, body, #map {
      height: 100%;
      width:100%;
      padding:0px;
      margin:0px;
   }

JavaScript

//////////////////////////////////////////////////////////////////////////////////////////////
//setting up the map//
//////////////////////////////////////////////////////////////////////////////////////////////

// set center coordinates
var centerlat = 34.05;
var centerlon = -118.25;

// set default zoom level
var zoomLevel = 10; 

// initialize map
var map = L.map('map').setView([centerlat,centerlon], zoomLevel);
//var map = L.map('map',{preferCanvas: true}).setView([centerlat,centerlon], zoomLevel);
 
// set source for map tiles
ATTR = '&copy; <a href="http://openstreetmap.org">OpenStreetMap</a> contributors, ' +
'<a href="http://creativecommons.org/licenses/by-sa/2.0/">CC-BY-SA</a> | ' +
'&copy; <a href="http://cartodb.com/attributions">CartoDB</a>';

CDB_URL = 'http://{s}.basemaps.cartocdn.com/light_all/{z}/{x}/{y}.png';

// add tiles to map
L.tileLayer(CDB_URL, {attribution: ATTR}).addTo(map);

//////////////////////////////////////////////////////////////////////////////////////////////
//creating some synthetic GeoJSON data//
//////////////////////////////////////////////////////////////////////////////////////////////

//initialize
var dotlayer;
var dots;
var dotcount = 50000;

//cheapo normrand function
function normish(mean, range) {
    var num_out = ((Math.random() + Math.random() + Math.random() + Math.random() - 2) / 2) * range + mean;
    return num_out;
}

//create geojson data with random ~normal distribution
function make_dots() {

    dots = {
        type: "FeatureCollection",
        features: []
    };

    for(var i=0;i<dotcount;++i) {

        //set up random variables
        x = normish(0, 2);
        y = normish(0, 2);
        
        //create points randomly distributed about center coordinates
        var g = { 
            "type": "Point",
            "coordinates": [ ((x*0.9) + centerlon), ((y*0.9) + centerlat)]
        };
        
        //create feature properties, with year roughly proportional to distance from center...