AmMaps - legend / zoom with 2 maps

Based on this demo: https://www.amcharts.com/demos/grouped-countries-map/

by Anton

HTML

<script src="https://www.amcharts.com/lib/3/ammap.js"></script>
<script src="https://www.amcharts.com/lib/3/maps/js/worldHigh.js"></script>
<script src="https://www.amcharts.com/lib/3/plugins/export/export.min.js"></script>
<link rel="stylesheet" href="https://www.amcharts.com/lib/3/plugins/export/export.css" type="text/css" media="all" />
<script src="https://www.amcharts.com/lib/3/themes/light.js"></script>

<div id="map1" class="mapdiv"></div>
<div id="map2" class="mapdiv"></div>
<div id="map3" class="mapdiv"></div>
<div id="map4" class="mapdiv"></div>

CSS

.mapdiv {
  display: inline-block;
  width: 48%;
  height: 300px;
}

JavaScript

for(var i = 1; i <= 4; i++)
	AmCharts.makeChart("map" + i, getMap());



// ----------------------------------------------
function getMap() {
	return {
    "type": "map",
    "theme": "light",
    "dataProvider": {
      "map": "worldHigh",
      "zoomLevel": 3.5,
      "zoomLongitude": 10,
      "zoomLatitude": 52,
      "areas": [ {
          "title": "Austria",
          "id": "AT",
          "color": "#67b7dc",
          "customData": "1995",
          "groupId": "before2004"
        }, {
          "title": "Ireland",
          "id": "IE",
          "color": "#67b7dc",
          "customData": "1973",
          "groupId": "before2004"
        }, {
          "title": "Denmark",
          "id": "DK",
          "color": "#67b7dc",
          "customData": "1973",
          "groupId": "before2004"
        }, {
          "title": "Finland",
          "id": "FI",
          "color": "#67b7dc",
          "customData": "1995",
          "groupId": "before2004"
        }, {
          "title": "Sweden",
          "id": "SE",
          "color": "#67b7dc",
          "customData": "1995",
          "groupId": "before2004"
        }, {
          "title": "Great Britain",
          "id": "GB",
          "color": "#67b7dc",
          "customData": "1973",
          "groupId": "before2004"
        }, {
          "title": "Italy",
          "id": "IT",
          "color": "#67b7dc",
          "customData": "1957",
          "groupId": "before2004"
        }, {
          "title": "France",
          "id": "FR",
          "color": "#67b7dc",
          "customData": "1957",
          "groupId": "before2004"
        }, {
          "title": "Spain",
          "id": "ES",
          "color": "#67b7dc",
          "customData": "1986",
          "groupId": "before2004"
        }, {
          "title": "Greece",
          "id": "GR",
          "color": "#67b7dc",
          "customData": "1981",
          "groupId": "before2004"
        }, {
          "title": "Germany",
          "id":...