It is my understanding that the FrameLayout will place everything in the upper left corner of its parent view (in this case, it is the top level view, or the screen. Adding the MapView and then the LinearLayout will place the LinearLayout (and its contents) on top of the MapView, which may obscure it. I am not sure if this is desired behavior for you or not.
I do not know what you are seeing, so perhaps you can give me (and the rest of this community!) some more details about what you are seeing and what it is that you want to see.
Hope this is helpful