For basic insurance, the premium regions are classified by the Federal Office of Public Health (FOPH) and these are binding for all insurers. The cantons/half-cantons constitute the main regions . Within cantons where the cost of claims varies widely, the FOPH has also defined a maximum of three premium regions.
For supplementary insurance, the premium regions depend on each insurance plan and the classification is different. For example, there is only one premium region for some products. It is therefore possible that only your basic insurance premium will change.