# Postcode Lookup JSON Files

This directory stores postcode expansion maps used by `PostcodeExpansionService`.

## Format

Each JSON file should contain a map of postcode prefix to list of full outward postcodes:

```json
{
  "BN": ["BN1", "BN2", "BN3"]
}
```

## Notes

- Keys are normalized to uppercase at load time.
- Values are normalized to uppercase and deduplicated.
- You can split data across multiple files (for example: `AB.json`, `BN.json`, `SW.json`).
- All `*.json` files in this directory are loaded and merged.
