Moving across town can change an auto insurance premium substantially without any change in the driver, the vehicle, or the record. Location is one of the strongest rating factors.
Insurance prices expected claims
A premium is an estimate of what the policy will cost the insurer, spread across everyone in a similar group and loaded for expenses and capital.
Anything that reliably predicts claim cost becomes a rating factor, provided regulators in that state permit its use.
Geography predicts strongly, which is why territory has been part of auto rating since long before modern data was available.
Frequency differs before severity does
Dense areas produce more collisions per mile driven, simply because there are more vehicles, more intersections, and more opportunities for contact.
Parking on a street rather than in a garage adds exposure to theft and to damage from other vehicles, neither of which involves the driver at all.
These are counts of events rather than costs per event, and they vary meaningfully across neighborhoods within a single metropolitan area.
Repair and medical costs vary locally too
The same damage costs different amounts to repair depending on local labor rates and shop availability, which differ between regions and between urban and rural areas.
Medical costs following injury vary similarly, and the share of claims involving injury differs with local crash patterns and speeds.
Litigation practices also vary by state, affecting how often claims are disputed and what they settle for, which flows into premiums for everyone in that state.
State rules govern what may be used
Insurance is regulated at the state level, and states differ on which factors are permitted, how territories may be drawn, and what filings are required.
Some states have restricted or banned particular rating factors, which changes how insurers distribute cost among their remaining customers in that state.
This is why a comparison of premiums between states measures regulation as much as risk, and why national averages describe no one in particular.
Territory is a group, not a judgment
A rating territory reflects the aggregate experience of policies in an area rather than any assessment of an individual driver.
A careful driver in a high-claim area is priced according to the group because insurers cannot observe carefulness directly, only its correlates.
Usage-based programs attempt to narrow that gap by measuring driving behavior directly, which shifts weight from where a car is kept toward how it is actually used.