Process mapping is a visualisation technique or method.
You can use this method to map the relationship between individual workflow steps, define the start, end and decision points within the flowchart and to describe the flow through various organisational units, thus creating a common view of the process to those involved.
The technique makes use of three different kind of diagrams or flowcharts: (1) the process relationship diagram, (2) the cross-functional flowchart and (3) the linear flowchart.
Besides using flow charting techniques, you can also add textual descriptions, comments and clarifying documents to create a clear picture.
The 'process relationship diagram' is used to create an overview of the whole organisation and shows how in general information, materials and resources, activities and funds flow from input to output.
It clarifies at a main system level the relationship within an organisation between its organisational units, as well as with its suppliers and customers.
This diagram is not used every single time, but can provide a first quick overview if the people on your improvement team are new to the organisation.
The 'cross-functional flowchart' is the diagram used most often and focuses on a single workflow and shows the flow through the process from one step to the next.
Swimlanes are used to give insight into  the roles and functions involved in the process.
Each lane represents a specific role or function.
Individual workflow steps are positioned within a lane and the steps are linked together with the use of arrow.
A 'linear flowchart' consecutively shows the entry conditions, input, practices or activities taking place and finally the resulting output and exit conditions of the process or workflow step, without taking the various functions or roles involved into account.
A 'linear flowchart' can provide clarification, but often the clarification is already provided in another format such as by adding a written description or linking a sample document to the flowchart.
By organising workshops in which a group of people actually involved in the process is brought together to create the 'process maps' as a team, you create a much better understanding of the current 'AS IS' situation as well as more easily discuss ways to improve to a 'SHOULD BE' or possibly even a  'COULD BE' situation.
The resulting flowcharts offer a starting point for discussions and possibly could be a way to finding improvement themes.
There are three ways to create process maps.
One way is to to it yourself.
If the process is known or straight forward, a map can be produced and presented to those involved for approval.
The advantage here is speed, but the downside is that detailed knowledge and experience may be lacking at any point.
Another way is to do the actual mapping activity together with those involved in the process.
This method is most effective if time is less important.
It creates more commitment of the staff involved, a common view of the total workflow for all involved is created which often is better understood.
Doing the activity together motivates people to actually accept or even propose improvements.
A 'process mapping' workshop is also a good team-building activity (a good facilitator is very important for this).
A last way to create the flowcharts is by using the interview technique.
A series of interviews with those involved (internal and external suppliers, contractors and internal and external customers) also makes the creation of a good flowchart possible.
After completion, the map can be presented to those interviewed and others involved for comments.
The interviewer must have a good knowledge of questioning and master the needed listening skills.