The Edit-Unlock Menu Option

When a raster map is loaded into the raster-editor the 
editor is locked.  You can not make any changes to the 
raster map until the editor is unlocked.  

Choosing this menu option will unlock the editor.  
You will notice that two things will happen when you 
unlock the editor: 1) the locked padlock symbol on the 
left-most button of the button-bar will turn into an 
unlocked padlock, and 2) the Unlock menu option will 
turn into the Unlock menu option.


