{
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "title": "One cell of the national bridge condition-rating transition table, or one reversal event",
  "type": "object",
  "additionalProperties": false,
  "required": [
    "unit",
    "component"
  ],
  "properties": {
    "unit": {
      "type": "string",
      "description": "The filing unit: a two-letter postal code for a state, the District of Columbia, Puerto Rico, Guam or the US Virgin Islands. It is the file the record came from, not a field inside it, because the file is the thing that guarantees it.",
      "x-origin": "redistributed",
      "x-source": "src:fhwa-national-bridge-inventory"
    },
    "component": {
      "type": "string",
      "description": "Which rating moved: d = deck (item 58), s = superstructure (item 59), b = substructure (item 60), c = culvert (item 62). The culvert scale has its own verbal descriptions in the Coding Guide, so a step of one on c does not mean the same thing as a step of one on d.",
      "x-origin": "redistributed",
      "x-source": "src:fhwa-national-bridge-inventory"
    },
    "year_from": {
      "type": [
        "string",
        "null"
      ],
      "description": "transitions.csv only. The earlier of the two annual snapshots. The later one is this plus one.",
      "x-origin": "redistributed",
      "x-source": "src:fhwa-national-bridge-inventory"
    },
    "rating_from": {
      "type": [
        "string",
        "null"
      ],
      "description": "transitions.csv only. The rating in the earlier snapshot, 0 to 9. Ratings coded N, and any other non-digit, are excluded from the table entirely rather than mapped to a number.",
      "x-origin": "redistributed",
      "x-source": "src:fhwa-national-bridge-inventory"
    },
    "rating_to": {
      "type": [
        "string",
        "null"
      ],
      "description": "transitions.csv only. The rating in the later snapshot.",
      "x-origin": "redistributed",
      "x-source": "src:fhwa-national-bridge-inventory"
    },
    "reconstruction_recorded": {
      "type": [
        "string",
        "null"
      ],
      "description": "transitions.csv only. 1 if item 106 (year reconstructed) changed between the two snapshots, or names a year within one year of the pair; 0 otherwise. This is NOT a record of whether work happened: the Coding Guide excludes from item 106 a long list of real work including emergency structural repair, retrofitting, added girders, deck overlays under a surfacing project and steel painting.",
      "x-origin": "built",
      "x-source": "src:aw-bridge-rating-transitions"
    },
    "inspection_date_advanced": {
      "type": [
        "string",
        "null"
      ],
      "description": "transitions.csv only. 1 if item 90 (date of last routine inspection) differs between the two snapshots, 0 if it is identical, 2 if either snapshot has no usable date. Under a 24-month inspection cycle reported into an annual file, 0 is an ordinary state and not an anomaly.",
      "x-origin": "built",
      "x-source": "src:aw-bridge-rating-transitions"
    },
    "count": {
      "type": [
        "string",
        "null"
      ],
      "description": "transitions.csv only. How many bridges made exactly this movement. The table is complete: summed over every row it is 49,764,872.",
      "x-origin": "built",
      "x-source": "src:aw-bridge-rating-transitions"
    },
    "structure_number": {
      "type": [
        "string",
        "null"
      ],
      "description": "reversals.csv only. Item 8, the state-assigned structure number, outer whitespace trimmed. Unique within a filing unit within a year, and not guaranteed stable across years: states renumber.",
      "x-origin": "redistributed",
      "x-source": "src:fhwa-national-bridge-inventory"
    },
    "year_up": {
      "type": [
        "string",
        "null"
      ],
      "description": "reversals.csv only. The earlier snapshot of the pair in which the rating rose.",
      "x-origin": "redistributed",
      "x-source": "src:fhwa-national-bridge-inventory"
    },
    "rating_before": {
      "type": [
        "string",
        "null"
      ],
      "description": "reversals.csv only. The rating before the rise.",
      "x-origin": "redistributed",
      "x-source": "src:fhwa-national-bridge-inventory"
    },
    "rating_peak": {
      "type": [
        "string",
        "null"
      ],
      "description": "reversals.csv only. The highest value reached during the excursion.",
      "x-origin": "redistributed",
      "x-source": "src:fhwa-national-bridge-inventory"
    },
    "year_back": {
      "type": [
        "string",
        "null"
      ],
      "description": "reversals.csv only. The snapshot in which the rating had returned to rating_before or lower.",
      "x-origin": "redistributed",
      "x-source": "src:fhwa-national-bridge-inventory"
    },
    "rating_after": {
      "type": [
        "string",
        "null"
      ],
      "description": "reversals.csv only. The value it returned to.",
      "x-origin": "redistributed",
      "x-source": "src:fhwa-national-bridge-inventory"
    }
  }
}