# Data Dictionary - US Firearm Background Checks (FBI NICS) - monthly by state, 1998-present, cleaned Parquet

**Units:** all `checks` values are in **checks**.  Times are UTC.

| column | type | description |
|---|---|---|
| `zone` | str | 2-letter US state / territory code (AL..WY, DC, GU, PR, VI, MP) |
| `ts` | timestamp (UTC) | First of the month |
| `checks` | int | Number of NICS firearm background checks initiated that month |
| `unit` | str | Unit (checks) |
| `res_min` | int | Native resolution (43200 = monthly) |

*Source: FBI National Instant Criminal Background Check System (NICS).*