At the heart of the airspace concept methodology lie Activities 7 through to 9 which have to do with the actual design of PBN Routes/Holds, the initial procedure design and the airspace volumes to protect the routes and sectorisation to manage the traffic.
Activities 7-8-9 do not and cannot follow a linear progression. Iteration is what anchors the three activities and binds them. Yes, on the first round, Activity 7 (route design) is done first, followed by Activity 8 (initial procedure design to check for feasibility) and at this point, the first iteration may be needed with Activity 7 as a desired route is unfeasible from a PANS-OPS perspective, and it has to be re-located or re-positioned.
When these iterations begin to mature, then Activity 9 is undertaken (design of the airspace volume and sectors), but certain constraints/realities may require the routes from Activity 7 to be moved either to reduce the amount of airspace needed to protect the planned flightpaths or to balance the traffic flows in each sector. This means that the relevant part of Activity 7 must be redone – and so the to and fro motion between the activities continues until something workable is achieved.
These iterations are not easy, particularly in airspaces where runways change frequently due to meteorological conditions, and where several operating scenarios have to be ready depending on wind/environmental requirements and so on.