<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent" android:layout_height="fill_parent">

    <com.google.android.maps.MapView
        android:id="@+id/mapView" android:layout_width="fill_parent"
        android:layout_height="fill_parent" android:enabled="true"
        android:layout_centerInParent="true" android:clickable="true"
        android:apiKey="your api key" />

    <Button android:layout_width="wrap_content"
        android:layout_height="wrap_content" android:text="Click"
        android:layout_alignParentRight="true"
        android:layout_alignParentBottom="true" android:id="@+id/clickBtn" />

</RelativeLayout>