Estoy tratando de ejecutar un mapa de Google simple, pero no funciona, solo muestra el fondo background.checked en el emulador y el dispositivo.

archivo xml: -

<fragment xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/map"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    class="com.google.android.gms.maps.SupportMapFragment"/>

Clase de Java

import android.os.Bundle; import
com.google.android.gms.maps.GoogleMap; import
com.google.android.gms.maps.SupportMapFragment; import
com.google.android.gms.maps.model.BitmapDescriptorFactory; import
com.google.android.gms.maps.model.LatLng; import
com.google.android.gms.maps.model.Marker; import
com.google.android.gms.maps.model.MarkerOptions;

public class LocationGB extends android.support.v4.app.FragmentActivity {     
    static final LatLng HAMBURG = new LatLng(53.558, 9.927); 
    static final LatLng KIEL = new LatLng(53.551, 9.993);
    private GoogleMap map;
     @Override protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_location);
        map = ((SupportMapFragment) getSupportFragmentManager().findFragmentById(android.R.id.content)).getMap();

        if (map!=null){
            Marker hamburg = map.addMarker(new MarkerOptions().position(HAMBURG)
                .title("Hamburg"));
            Marker kiel = map.addMarker(new MarkerOptions()
                .position(KIEL)
                .title("Kiel")
                .snippet("Kiel is cool")
                .icon(BitmapDescriptorFactory
                .fromResource(R.drawable.ic_launcher))); 
        }
    } 
}