A postal code is not a municipality
Ask someone in Zürich where they live and many will answer "8006" — as if the postal code named their municipality. It doesn't. A PLZ is a Swiss Post routing number, not a political boundary. One postal code can cross several municipalities, and one municipality can have several postal codes.
That is not a rare edge case. Out of Switzerland's 3'190 postal codes, a large share are shared between municipalities:
1'220 of 3'190 Swiss postal codes cover more than one municipality.
So 1'220 postal codes — 38.2% of them — have a delivery area that reaches into more than one municipality. An encyclopedia can tell you this happens; here you can see exactly where, and click through to each municipality.
The extreme case
The single most fragmented postal code in the country, 1148, spans 8 separate municipalities on its own:
Postal code 1148 alone is split across 8 separate municipalities — each with its own page:
| Municipality | Canton | BFS no. |
|---|---|---|
| Chavannes-le-Veyron | VD | 5475 |
| Cuarnens | VD | 5479 |
| La Chaux (Cossonay) | VD | 5474 |
| La Praz | VD | 5758 |
| L'Isle | VD | 5486 |
| Mauraz | VD | 5488 |
| Moiry | VD | 5490 |
| Mont-la-Ville | VD | 5491 |
Every municipality in that table is a distinct political body with its own council, its own tax rate and its own BFS number — all sharing one postal code because that is simply how the post is routed through the valley.
Why it matters
If you infer a municipality from a postal code, you can pin the wrong tax rate, the wrong vote result or the wrong mayor to an address. Figures published "by postal code" quietly average several municipalities together. The fix is to treat the postal code as what it is — a delivery key — and to look the municipality up separately.
For how the postal code, locality, municipality and canton actually fit together, see how Swiss addresses are structured; for why the list of municipalities itself keeps shrinking, see why the number of municipalities keeps falling.