1. Choose the unit and write down the precedence
Geography, vertical, account size or a mix. If you use more than one, record which rule wins when two apply, because that ambiguity is where duplicate calling comes from.
2. Count what is actually there
Pull accounts and open leads by the proposed unit before deciding anything. Most first drafts collapse at this step, which is the cheapest place for them to collapse.
3. Model workload, not headcount of customers
Multiply accounts by the contact frequency each tier needs, and add travel time for field patches. Compare the totals across territories rather than the account counts.
4. Balance for opportunity as well as effort
A territory should contain enough addressable revenue for the target attached to it. Equal effort with unequal opportunity is the fastest route to losing a good rep.
5. Publish the rules and switch on assignment
Turn the definitions into routing rules so new enquiries land with one owner automatically. A plan that depends on people remembering it is not a plan.
6. Review coverage quarterly, realign rarely
Look at uncontacted accounts, overlaps and gaps every quarter. Change ownership only when the evidence is strong, since continuity has real value to customers.