Boundary changes follow statutory procedures that vary substantially by state and by the type of units involved.
Methods. Petition by property owners; resolution of the affected units; referendum of the affected electors; and in some states a boundary commission process with criteria and a hearing.
Criteria. Contiguity, the ability of the annexing unit to provide services, the fiscal effect on both units, consistency with planning, and the wishes of the affected residents.
Conditional transfers and agreements. Many states authorise agreements between units to transfer property, share revenue, or fix boundaries for a term — frequently a more workable solution than a contested annexation.
Service commitments. The annexing unit’s obligation to extend services within a stated period, sometimes enforceable by the property owners.
Zoning on annexation. The annexing unit’s zoning applies, subject in some states to a period during which the prior classification continues, and to protections for existing uses.
Debt and assets. Allocation of the detaching unit’s debt attributable to the transferred territory, and the disposition of infrastructure.
Litigation. Challenges are brought on procedure and on the criteria, on short deadlines, and courts are deferential where the statutory process was followed.