こんにちは。
Google Maps で kml データ表示してみました。普通は google.maps.KmlLayer 利用だと思いますが、geoxml3 を利用してローカルファイルを読み込んでみました。

下記表示例は "KML Layers" (Google Maps JavaScript API) のデータを利用。

<!DOCTYPE html>
<html>
<head>
<meta http-equiv="content-type" content="text/html; charset=utf-8">
<meta charset="utf-8">
<title>Reading KML Files with Google Maps</title>
<style type="text/css">
html, body { height: 100%; margin: 0; padding: 0;}
# map_canvas { height: 100%;}
.geoxml3_infowindow * {font-size: 90%; margin: 0}
</style>

<script type="text/javascript" src="http://maps.google.com/maps/api/js?sensor=false"></script>
<script type="text/javascript" src="http://geoxml3.googlecode.com/svn/branches/kmz/geoxml3.js"></script>

<script type="text/javascript">
var map = null;
var geoXml = null;
var par = {lon: 140.000, lat: 35.500, zoom: 10};

function gpos(obj) {
    return new google.maps.LatLng(obj['lat'], obj['lon']);
}

function initialize() {
	var maptype = google.maps.MapTypeId.ROADMAP;
	var mapOptions = {
		center: gpos(par),
		zoom: par['zoom'],
		mapTypeId: maptype,
		scaleControl: true,
	};
    var mapDiv = document.getElementById('map_canvas');
	map = new google.maps.Map(mapDiv, mapOptions);
 
	var infowindow = new google.maps.InfoWindow({});
	geoXml = new geoXML3.parser({
	                map: map,
	                infoWindow: infowindow,
	                singleInfoWindow: true,
	                zoom: true,
	            });
};

function readFiles(files) {
    for (var i = 0, file; file = files[i]; i++) {
        readKML(file);
    }
}

function readKML(inFile) {
    var reader = new FileReader();
    reader.onload=function(e){
        geoXml.parseKmlString(reader.result);
    };
    reader.readAsText(inFile, 'utf-8');
}

function handleFileSelect(evt) {
    readFiles(evt.target.files);
    document.getElementById('form').style.display = "none";
}

</script>
</head>
<body onload="initialize()">
  <form id="form" style="height:32px;background-color:#f0f0f0;"> &nbsp;
  <input type="file" id="file" name="file" title="Load local kml file" accept='.kml' />
  </form>
  <script>document.getElementById('file').addEventListener('change', handleFileSelect, false);</script>
  <div id="map_canvas"></div>
</body>
</html>