how can i show a google map in custom post type

$prop_mapaddress contains your textfield value:

<?php 
    if(isset($prop_mapaddress)) {
        global $post;
        global $wpdb;

        $fromat_address = trim($prop_mapaddress);
        $fromat_address = str_replace(" ","+",$fromat_address);
        $address_obj = file_get_contents("http://maps.googleapis.com/maps/api/geocode/json?address=".$fromat_address."&sensor=false");
        $address_obj =json_decode($address_obj);
        $latitude = $address_obj->results[0]->geometry->location->lat;
        $longitude = $address_obj->results[0]->geometry->location->lng;            
    ?>       
        <script>        
            var geocoder;       
            var map;      
            var lat = "<?php echo $latitude ?>";       
            var lng = "<?php echo $longitude;  ?>";

            function initialize() {       
                geocoder = new google.maps.Geocoder();       
                var latlng = new google.maps.LatLng(lat, lng);       
                var mapOptions = {        
                    zoom: 15,        
                    center: latlng,        
                    mapTypeId: google.maps.MapTypeId.ROADMAP       
                }        
                map = new google.maps.Map(document.getElementById('map-canvas'), mapOptions);        
            } // map-convas would be id of div you want to show your map in  

            google.maps.event.addDomListener(window, 'load', initialize);       
        </script>      
        <?php        
    }
?>

Also don’t forget to enqueue Google API script before actually loading map:

wp_enqueue_script('google-map-api','https://maps.googleapis.com/maps/api/js?v=3.exp&sensor=false');