Forward /bacward order for objects

[Håvard Fosså]

I am designing a status view for a sun shading project, showing the status of the blinds in a facade view.  The interface is showing the actual blind position, the slat angle and the state of control - manual or automatic.

There is also several blocking object for each floor /facade, where the blinds can be blocked.  I want to have information about present blocking status for the following blocking objects which  have the following priority:

1. Fire alarm 
   
2. Service 
   
3. Wind 
   
4. Window cleaning
   
5. Blind cleaning  
   

I tried to do this using suitable icons for active blocking.  For showing the state of no blocking i made a custom icon with a transparent background, showing nothing when the blocking is inactive.  Then i place all the icons in the same position in top of each other, with the icon with  highest in priority in front, and those with lower priority backward.

I thought the backward/forward order for the icons was based on when they were created, but i can not find how to control of the backward /forward order for the icons.  

In graphic applications, eg. Visio and Publisher, there is a move forward /move backward button to control this behavior.

My question:  How is the backward / forward order for icons defined, and is there anyway to control which icon will be in front?