In the XAML I have defined a grid with three columns and one row. The first column contains data, the second a gridsplitter and the third the map control. If I move the slider to the left toward the first column I can see the columns adjust their size. If I attempt to move it toward the right the splitter does not move and the column are not resized. The splitter is highlight so I know it is getting focus. I see the double arrow showing the splitter going into the map column but again the columns are not adjusting width as I expect and the splitter does not move. It look like the map control will increase in size if its container control size is increased but will not decrease if the container control is decreased. I'm see the same behavior if I expand my main application to span the width of my two screen and then display the map, if I size my application window to fit a single screen the map does not change size. Is this expected behavior or do I have a map property set correctly? Using the map control without any properties set in the XAML.