GNIS — the federal standard for geographic coordinates — systematically points to ICW channel references instead of ocean entrances. We used satellite imagery and vision AI to find and fix it.
Eric Whyne · Data Machines · February 20, 2026
📄 Download PDFGNIS classifies inlets as “Channel” features — so coordinates point to the channel (ICW), not the ocean entrance where boats actually transit.
Points to a spot on the Intracoastal Waterway — 0.3 to 8.5 nm from the actual ocean entrance.
Where boats actually cross the bar, face breaking waves, and need precise depth data to survive.
From manual discovery to automated verification — each approach built on the limitations of the last.
Developer notices Shallotte Inlet's coordinates are wrong. Effective but impractical at scale — 15-20 hours for 130 inlets.
Systematic query confirms bias is widespread. But GNIS IS the ground truth — no alternative database to compare against.
Built /inlets page overlaying coordinates on Mapbox satellite imagery. Human can see the problem instantly — but still manual.
Satellite imagery + vision AI audits all 130 inlets in 10 minutes. 95 corrections deployed to production.
Coarse screening with one model, pixel-precise refinement with another.
Initial developer reaction: “A tool that flags 96% of inputs must be broken.” Manual verification proved: the AI was right.
Key insight: vision models are better at spatial identification within an image than at geographic coordinate estimation from pixel positions.
The biggest barrier wasn't model accuracy — it was the team's reluctance to trust consistent findings that challenged assumptions about a federal database. When a tool built to detect a known bias detects that bias consistently, the appropriate response is verification, not dismissal.
When a boater navigates to an inlet in deteriorating conditions, the difference between the ocean mouth and a point on the ICW is not academic — it's the difference between entering safely and searching in breaking seas.
USGS should review and update GNIS coordinates for coastal inlets
A verified ocean-entrance coordinate dataset should be published as open data
Federal agencies should adopt vision AI as a routine QA tool for geographic databases