Not every value in fldzone describes a flood risk. Three cases mark areas the FIRM does not assign a hazard rating to. Handle them explicitly so they are never mistaken for a low-risk classification.

OPEN WATER

fldzone = 'OPEN WATER'

The polygon is a body of water — ocean, bay, large lake, or wide river surface — rather than land subject to a flood-hazard rating. FEMA maps these areas so the FIRM is spatially complete, but assigning a flood zone to open water is meaningless.

• No BFE; staticbfe is NULL.
• A parcel tagged OPEN WATER typically has geometry that overlaps a mapped water body (e.g. submerged land, riparian or littoral parcels, or slivers extending into water).

AREA NOT INCLUDED

fldzone = 'AREA NOT INCLUDED'

The area was deliberately excluded from the flood study. This most often occurs where a community did not participate in the study, at jurisdictional boundaries, or where mapping was left to an adjacent panel. It is an administrative gap, not a statement that the area is safe or unstudied-but-possible (that would be D).

• No BFE; staticbfe is NULL.

NULL

fldzone IS NULL

The parcel has no intersecting NFHL polygon at all. This happens when:

• the county has no effective NFHL data digitized, or
• the parcel lies entirely outside every mapped flood-hazard area on the applicable panel.

A NULL fldzone means "no FEMA flood data was joined to this parcel" — it is an absence of data, distinct from D (mapped, but risk undetermined) and from unshaded X (mapped, minimal risk). When fldzone is NULL, the companion columns zonesubty, staticbfe, firmid, and firmdate are NULL as well.

In the data

-- Parcels with a mapped high-risk zone (the SFHA)
SELECT count(*)
FROM   lr_parcel_us
WHERE  fldzone IN ('A','AE','AH','AO','AR','A99','V','VE');

-- Parcels with no FEMA flood data joined
SELECT count(*)
FROM   lr_parcel_us
WHERE  fldzone IS NULL;

See also: the flood-zone overview and the Table Schema.