Map the Items that drive the process. 
What is an Item?  An item is something physical. It is something you can see. An item is a form, an electronic file, an email, a document, a spreadsheet, a CD, a database, an application, a log sheet, a reference book, etc. We record, transmit and store information on items.  Items convey the information that drives our processes.  Items give substance to a process map.  They enable us to assemble an otherwise nebulous collection of activities into an organized, reality-based system.  Each Item is charted as a separate horizontal flow line that is identified at its beginning with a label.

What items are involved in the process?  No other method addresses this basic question!  How can you understand a process if you don't know the items that drive it?