XML : Android Align LinearLayout at Bottom not Working

I have this LinearLayout and in it is a Map Fragment and this all works but I cannot get the linear layout to align to the bottom of the screen for some reason. Here is my xml:

  <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"      xmlns:tools="http://schemas.android.com/tools"      android:layout_width="match_parent"      android:layout_height="match_parent"      android:orientation="vertical"      tools:context=".MainActivity"      android:baselineAligned="false"      android:weightSum="1"      android:background="@mipmap/background_colour">        <LinearLayout          android:orientation="vertical"          android:layout_width="30dp"          android:layout_height="31dp"          android:weightSum="1"          android:id="@+id/back_button"          android:background="@drawable/navigation_back"          android:layout_marginTop="20dp"          android:layout_marginLeft="10dp">        </LinearLayout>        <LinearLayout          android:orientation="horizontal"          android:layout_width="match_parent"          android:layout_height="wrap_content"          android:layout_weight="0.31">            <TextView              android:layout_width="wrap_content"              android:layout_height="wrap_content"              android:textAppearance="?android:attr/textAppearanceLarge"              android:text="Large Text"              android:id="@+id/textView7" />      </LinearLayout>        <LinearLayout          android:orientation="horizontal"          android:layout_width="match_parent"          android:layout_height="wrap_content"          android:layout_weight="0.30">            <TextView              android:layout_width="wrap_content"              android:layout_height="wrap_content"              android:textAppearance="?android:attr/textAppearanceLarge"              android:text="Large Text"              android:id="@+id/textView6" />      </LinearLayout>        <LinearLayout          android:id="@+id/lay"          android:orientation="horizontal"          android:layout_width="match_parent"          android:layout_alignParentBottom="true"          android:layout_height="wrap_content"          android:layout_weight="3.5">            </LinearLayout>      </LinearLayout>    

The LinearLayout I am trying to align is the id: "lay" one.