Displaying N levels of organisational hierarchy intuitively

Question

I need to display top-down hierarchical data in a web browser that represents the geography of a large organisation. The data looks like this (except the actual list is enormous with 8000 staff across 47 sites with nearly 700 departments):

London
  South
     Finance
     Operations
  West
     Billing
        Credit Approval
        Reclaims
        Processors
Leeds
   Corporate
      Directors
      Vice

Within the web site, a user needs to select members of staff by either clicking All next to a specific level, or by interrogating the structure and choosing Specific/All User(s) from each layer.

Can anyone offer any advice or inspiration on the best way to achieve this in an intuitive fashion? How do the 'big boys' like SAP and Oracle achieve a solution? Can anyone share any screen grabs to show this?

I thought of using nested drop down lists, like this:

1. User selects a layer
2. Drop down list appears underneath with all child layers
3. Select list appears to one side containing users from selected layer (with Add All / Add Selected links

It still feels a bit clumsy though, especially if someone needed a more complex selection, such as:

All users from West, plus
No users from Billing, plus 
Selected users from Credit Approval

I've done research but not turned up much. Jeff Atwood suggests tags instead of hierarchies (flat lists), but I don't think that would work in this instance as the hierarchy itself is important. Treeviews as an alternative don't seem to geared toward effective real estate, and there's the old favourite of chained select lists...

Answer 1

I have worked a little on SAP, sap does not have a graphical representation for such a thing, it usually deals with C.C. numbers or departments.

I would go with a TreeView titled "Filter" and a ListView titled "Selected", the tree view has the locations and departments. Users can select a department/location and then simply click on an arrow or a plus sign to add the selected group/location to the "Selected" list.

For the selected users part, I think this is not a very common selection, hence add that option to a context menu when clicked on a department, a window with employees in that department will show, once done it

BTW, we have an internal system that does exactly this, and I have never heard a complaint from any user regarding any confusion.