Dynamically adding cities to the map

HTML

<script type="text/javascript" src="http://www.amcharts.com/lib/3/ammap.js"></script>
<script type="text/javascript" src="http://www.amcharts.com/lib/3/maps/js/worldLow.js"></script>
<script type="text/javascript" src="http://www.amcharts.com/lib/3/themes/none.js"></script>
<div id="chartdiv"></div>
<div id="selector">
    <select id="cities"></select>
    <input type="button" value="Add selected city" onclick="addCity();" />
</div>

CSS

body {
    font-family: Verdana;
    font-size: 14px;
    padding: 10px;
}
#chartdiv {
	width	: 100%;
	height	: 500px;
}
#selector {
    position: absolute;
    top: 20px;
    right: 20px;
    background: rgba(255, 255, 255, 0.7);
    padding: 10px;
    font-size: 16px;
}
#selector input, #selector select {
    padding: 5px;
}

JavaScript

// a list of available cities
var cities = [{
      title: "Vienna",
      latitude: 48.2092,
      longitude: 16.3728
    }, {
      title: "Minsk",
      latitude: 53.9678,
      longitude: 27.5766
    }, {
      title: "Brussels",
      latitude: 50.8371,
      longitude: 4.3676
    }, {
      title: "Sarajevo",
      latitude: 43.8608,
      longitude: 18.4214
    }, {
      title: "Sofia",
      latitude: 42.7105,
      longitude: 23.3238
    }, {
      title: "Zagreb",
      latitude: 45.8150,
      longitude: 15.9785
    }, {
      title: "Pristina",
      latitude: 42.666667,
      longitude: 21.166667
    }, {
      title: "Prague",
      latitude: 50.0878,
      longitude: 14.4205
    }, {
      title: "Copenhagen",
      latitude: 55.6763,
      longitude: 12.5681
    }, {
      title: "Tallinn",
      latitude: 59.4389,
      longitude: 24.7545
    }, {
      title: "Helsinki",
      latitude: 60.1699,
      longitude: 24.9384
    }, {
      title: "Paris",
      latitude: 48.8567,
      longitude: 2.3510
    }, {
      title: "Berlin",
      latitude: 52.5235,
      longitude: 13.4115
    }, {
      title: "Athens",
      latitude: 37.9792,
      longitude: 23.7166
    }, {
      title: "Budapest",
      latitude: 47.4984,
      longitude: 19.0408
    }, {
      title: "Reykjavik",
      latitude: 64.1353,
      longitude: -21.8952
    }, {
      title: "Dublin",
      latitude: 53.3441,
      longitude: -6.2675
    }, {
      title: "Rome",
      latitude: 41.8955,
      longitude: 12.4823
    }, {
      title: "Riga",
      latitude: 56.9465,
      longitude: 24.1049
    }, {
      title: "Vaduz",
      latitude: 47.1411,
      longitude: 9.5215
    }, {
      title: "Vilnius",
      latitude: 54.6896,
      longitude: 25.2799
    }, {
      title: "Luxembourg",
      latitude: 49.6100,
      longitude: 6.1296
    }, {
      title: "Skopje",
      latitude: 42.0024,
      longitude: 21.4361
    }, {
      title: "Valletta",
      latitude:...