quadtrees, what are they good for?

So hit the button in the bottom left to start adding points, then if you hold down shift and draw a box it'll running a bounding box query on that area and limit the map to that.

<!DOCTYPE html>
<meta charset="utf-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge,chrome=1">
    <meta name="viewport" content="width=1024, user-scalable=no">
    <style>
      html { height: 100% }
      body { height: 100%; margin: 0; padding: 0;}
      #map{ height: 100% }
      .leaflet-cluster-anim .leaflet-marker-icon, .leaflet-cluster-anim .leaflet-marker-shadow {
    -webkit-transition: -webkit-transform 0.25s ease-out, opacity 0.25s ease-in;
  -moz-transition: -moz-transform 0.25s ease-out, opacity 0.25s ease-in;
	-o-transition: -o-transform 0.25s ease-out, opacity 0.25s ease-in;
	transition: transform 0.25s ease-out, opacity 0.25s ease-in;
	}
	.marker-cluster-small {
	background-color: rgba(181, 226, 140, 0.6);
	}
.marker-cluster-small div {
	background-color: rgba(110, 204, 57, 0.6);
	}

.marker-cluster-medium {
	background-color: rgba(241, 211, 87, 0.6);
	}
.marker-cluster-medium div {
	background-color: rgba(240, 194, 12, 0.6);
	}

.marker-cluster-large {
	background-color: rgba(253, 156, 115, 0.6);
	}
.marker-cluster-large div {
	background-color: rgba(241, 128, 23, 0.6);
	}

.marker-cluster {
	background-clip: padding-box;
	border-radius: 20px;
	}
.marker-cluster div {
	width: 30px;
	height: 30px;
	margin-left: 5px;
	margin-top: 5px;

text-align: center;
	border-radius: 15px;
	font: 12px "Helvetica Neue", Arial, Helvetica, sans-serif;
	}
.marker-cluster span {
	line-height: 30px;
	}
    </style>
<link rel="stylesheet" href="https://cdn.leafletjs.com/leaflet-0.5.1/leaflet.css" />
<title>Quadtree madness</title>
<div id="map"></div>
<script src="https://d3js.org/d3.v3.js"></script>

quadtree = d3.geom.quadtree(p.map(function(v,i){return {x:v[0],y:v[1],all:v};}));
        
    };
    this.bbox=function(blat1,blng1,blat2,blng2){
        if(!blat1){
            return p;
        }
        var out = [];
        quadtree.visit(function(quad, lat1, lng1, lat2, lng2){
            if(((blat1>lat2)&&(blat2>lat2))||((blat1<lat1)&&(blat2<lat1))||((blng1>lng2)&&(blng2>lng2))||((blng1<lng1)&&(blng2<lng1))){
                return true;
            }else if(((blat2>=lat2)&&(blng2>=lng2)&&(blat1<=lat1)&&(blng1<=lng1))){
                out.push(quad);
                return true;
            }
        });
        var pts = [];
        function getPt(quad){
            if(quad.point){
                pts.push(quad.point.all);
            }
            if(!quad.leaf&&quad.nodes.length>0){
                quad.nodes.forEach(getPt);
            }
        }
        out.forEach(getPt);
        return pts;
    };
}
var m = L.map("map").setView([42.3164, -71.7],9);

//make the map

L.tileLayer("https://{s}.tile.stamen.com/watercolor/{z}/{x}/{y}.jpg",{minZoom:4,maxZoom:12,attribution:'Map tiles by <a href="https://stamen.com">Stamen Design</a>, <a href="https://creativecommons.org/licenses/by/3.0">CC BY 3.0</a> &mdash; Map data &copy; <a href="https://openstreetmap.org">OpenStreetMap</a> contributors, <a href="https://creativecommons.org/licenses/by-sa/2.0/">CC-BY-SA</a>'}
    ).addTo(m);
	
//add a tileset

//generate 60k random points
var pts = new L.MarkerClusterGroup();
pts.addTo(m);

var qt;
var bbox;
function morePoints(lat,lng){
    var randomLat = d3.random.normal(lat, .15),
    randomLng = d3.random.normal(lng, .5);
    var points = d3.range(2000).map(function() { return [randomLat(), randomLng()]; });
    if(!qt){
        qt = new Quadtree(points);
    }else{

qt.add(points);

}
    redoBox(bbox);

}

var BoxSelect = L.Handler.extend({
    initialize: function (map) {
		this._map = map;
		this._container = map._container;
		this._pane = map._panes.overlayPane;
	},

addHooks: function () {
		L.DomEvent.on(this._container, 'mousedown', this._onMouseDown, this);
	},

removeHooks: function () {
		L.DomEvent.off(this._container, 'mousedown', this._onMouseDown);
	},

_onMouseDown: function (e) {
		if (!e.shiftKey || ((e.which !== 1) && (e.button !== 1))) { return false; }

L.DomUtil.disableTextSelection();

this._startLayerPoint = this._map.mouseEventToLayerPoint(e);

this._box = L.DomUtil.create('div', 'leaflet-zoom-box', this._pane);
		L.DomUtil.setPosition(this._box, this._startLayerPoint);

//TODO refactor: move cursor to styles
		this._container.style.cursor = 'crosshair';

L.DomEvent
		    .on(document, 'mousemove', this._onMouseMove, this)
		    .on(document, 'mouseup', this._onMouseUp, this)
		    .preventDefault(e);

this._map.fire("boxselectstart");
	},

_onMouseMove: function (e) {
		var startPoint = this._startLayerPoint,
		    box = this._box,

layerPoint = this._map.mouseEventToLayerPoint(e),
		    offset = layerPoint.subtract(startPoint),

newPos = new L.Point(
		        Math.min(layerPoint.x, startPoint.x),
		        Math.min(layerPoint.y, startPoint.y));

L.DomUtil.setPosition(box, newPos);

// TODO refactor: remove hardcoded 4 pixels
		box.style.width  = (Math.max(0, Math.abs(offset.x) - 4)) + 'px';
		box.style.height = (Math.max(0, Math.abs(offset.y) - 4)) + 'px';
	},

_onMouseUp: function (e) {
		this._pane.removeChild(this._box);
		this._container.style.cursor = '';

L.DomUtil.enableTextSelection();

L.DomEvent
		    .off(document, 'mousemove', this._onMouseMove)
		    .off(document, 'mouseup', this._onMouseUp);

var map = this._map,
		    layerPoint = map.mouseEventToLayerPoint(e);

if (this._startLayerPoint.equals(layerPoint)) { return; }

var bounds = new L.LatLngBounds(
		        map.layerPointToLatLng(this._startLayerPoint),
		        map.layerPointToLatLng(layerPoint));

map.fire("boxselectend", {
			boxSelectBounds: [bounds.getSouthWest().lat,bounds.getSouthWest().lng,bounds.getNorthEast().lat,bounds.getNorthEast().lng]
		});
	}
});
m.boxZoom.disable();
var boxSelect = new BoxSelect(m);
boxSelect.enable();

m.on("boxselectend",function(e){redoBox(e.boxSelectBounds);});

</script>

Modified http://d3js.org/d3.v3.js to a secure url

Modified http://cdn.leafletjs.com/leaflet-0.5.1/leaflet.js to a secure url

Updated missing url https://raw.github.com/calvinmetcalf/Leaflet.markercluster/master/dist/leaflet.markercluster.js to https://cdn.jsdelivr.net/gh/calvinmetcalf/leaflet.markercluster/dist/leaflet.markercluster.js

https://d3js.org/d3.v3.js

https://cdn.leafletjs.com/leaflet-0.5.1/leaflet.js

https://raw.github.com/calvinmetcalf/Leaflet.markercluster/master/dist/leaflet.markercluster.js