The Ground Underneath the Map

By Zacharias · Principal

Reference-Frame Modernization, Vertical Land Motion, and the Hidden Basis Risk in Insurance

ISSUED 26 MAY 2026 · INSURANCE DESK · ZACHARIAS, PRINCIPAL · AUDITED AGAINST AEGEAN-OS

THE DOCUMENT

NumberAIG-INS-26-003

FormerlyPMR-2026-0526-GLOBAL-004

ProductAssessment · Series part 3

Issued2026-05-26

Pages13

DistributionPublic release

TimelinessDURABLE

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HOW TO CITE

Aegean Intelligence Group, “The Ground Underneath the Map,” AIG-INS-26-003, The Aegean Register, 26 May 2026.

SERIES · THE INSURANCE SEQUENCE

Part 3 of 3. The other parts: Part 1, When the Models Met Reality and Part 2, The Uninsurable Frontier.

Abstract

The flood-map regime rests on a reference frame the geodetic agencies are actively rebuilding. End of 2026, every elevation moves; Gulf and Southeast Coast relative sea-level is already accelerating past 10 mm/yr. Five million NFIP policies sit on a static-planet assumption.

Key judgments

KJ-1HIGH

The NSRS transition from NAD 83 and NAVD 88 to NATRF2022 and NAPGD2022 is structurally consequential for any insurance product whose pricing or eligibility depends on elevation relative to a fixed datum.

KJ-2HIGH

Vertical land motion is locally large relative to insurance flood-map precision: New Orleans west-bank subsidence exceeds 20 mm/yr in places and Houston-Galveston subsidence affects 12,000 square kilometers.

KJ-3HIGH

US Southeast and Gulf Coast relative sea-level rise has accelerated to rates an order of magnitude above the historical baseline, driven by absolute rise, the AMOC-response sterodynamic effect, and local subsidence.

KJ-4MODERATE

The cadence mismatch between reference-frame revision, regulatory model approval, and event arrival is the structural exposure; carriers locked to a given datum vintage carry concentrated calibration risk in the transition window.

Key stats

Source registry33 entries

Judgments4

Confidence3 HIGH / 1 MOD

Pages13

Issued 2026-05-26Public releaseDURABLEAIG-INS-26-003

Cover

FORWARD CLAIMS · DATED TO PUBLICATION · SCORED ON THE SCORECARD →

ID	Statement	p	Made on	Resolves by	Status
CLM-2026-013	During the transition window between formal NAPGD2022 release and full FEMA flood-map conversion (an estimated five years), properties will be rated, surveyed, and elevation-certified under mixed datum vintages with conversion offsets handled jurisdiction-by-jurisdiction.	0.85	2026-05-26	2031-12-31	Locked
CLM-2026-015	Parametric policy language issued during the 2026 to 2031 NSRS transition window will need to specify which datum applies, with formal conversion provisions, or contractual triggers will drift from physical signals by the conversion offset. We expect this to become a standard policy-language addition by 2027.	0.65	2026-05-26	2027-12-31	Locked
CLM-2026-022	Baseline is the most likely twelve-month path.	0.85	2026-05-26	2027-05-26	Locked

A claim is entered in the brief's own words and carries its publication date and the day it entered the ledger: the register's briefs on 8 September 2026, when the standard was first applied; the forward benchmark on the day it was locked. It resolves only against a dated public source. The scoring rule is on the Methodology page.

SOURCES & METHOD

Public-source synthesis exclusively, drawing on NOAA, NASA, USGS, National Geodetic Survey, IERS, ITRF/IGN, FEMA, and FHFA materials plus peer-reviewed geophysics and geodesy literature (Journal of Geodesy, GRL, JGR, Wiley Groundwater). Claims are structured as six key judgments with explicit confidence levels and superscript citations into a 33-entry source registry, with each section closing in an assessment stating confidence and rationale.

Limitations: The public record contains no explicit federal policy guidance on treating reference-frame revision in insurance rating, so the regulatory direction will not be visible until the first NGS and FEMA joint advisory after the NAPGD2022 release.

SOURCE REGISTRY: 33 ENTRIES13 PAGESTIMELINESS: DURABLE

Estimative language in this report follows the firm’s published standard: judgments carry HIGH, MODERATE, or LOW confidence, and each carries its rationale in the full report. The framework, source tiers, and anti-fabrication perimeter are public on the methodology page. Corrections issue as numbered addenda.