What statement are you using to bring that menu entry to its position? Eclipse uses Contribution URLs like: menu:org.eclipse.search.menu?after=contextMenuActionsGroup . That means "in the menu Search Menu place this entry after the group contextMenuActionsGroup .
In your case this would be something like: menu:my.path.map?after=mapGroup
If you do not know the path to your menu, you can use the shortcut Alt+Shift+F2 to select the menu entry before the group and check its path.