Why We Care About
the Bottom of the Sea.

Here is a fact that surprises people the first time they hear it. A route can be entirely made of water, nothing but open sea the whole way, and still be a genuinely bad route. Water is not automatically safe just because it is not land.

The land problem is not the only problem

We have written before about what happens when coastline data is too coarse to see rivers and narrow straits properly. That is a real problem, and a real one we fixed. But it only covers one half of what a route actually needs to avoid. Land is easy to reason about. Water is not uniform at all. Some of it is six thousand meters deep. Some of it, still technically water, is barely deep enough to float a small fishing boat, let alone a loaded cargo vessel that needs several meters of clearance beneath the hull just to stay off the bottom.

What bathymetry actually is

Bathymetry is the depth and shape of the seafloor, mapped the same way land elevation gets mapped, just underwater and much harder to measure directly. You cannot look at the bottom of the ocean from a satellite the way you can look at a mountain. Shoals, reefs, sandbars, and shallow banks all show up as ordinary water on a basic map. A vessel does not care that a hazard is technically water. It cares whether there is enough depth beneath it.

GEBCO2020, the dataset behind the numbers

GEBCO is a real, long running international effort to chart the depth of the entire ocean floor, combining actual ship soundings with satellite derived data, published openly and updated over time. GEBCO_2020 is the specific release our Ocean Graph Engine checks every navigable cell against.

The real number from that check, already published in detail elsewhere on this blog, is worth repeating here. Of the 24,140 cells generated for the full Indonesian archipelago, 22,841 came back navigable after a real depth lookup. The remaining roughly 1,300 were technically water on the map, and were marked not navigable anyway, because they were not deep enough to trust with a real vessel.

Thirteen hundred cells, all water, none of them safe. That gap is exactly what bathymetry is for.

Why this changes what a route can look like

A route that looks like the shortest path across open water can quietly cross a shoal or a shallow bank that a coastline map alone would never flag, because it is not land, it is just shallow. Depth data is what catches that before a fleet does, not after.

The same lesson, a different layer

Depth data has its own resolution limits too, the same way coastline data does. A shoal thin enough to slip between two sample points is still a real risk even inside a trusted, respected dataset. We treat it the same way we treat every other data source that matters to a route. Checked, tested, never assumed correct just because it comes from somewhere reputable. We would rather over check a source we trust than trust it blindly.

Where this stands

Depth checking is part of the Ocean Graph Engine, the same system we have described in detail elsewhere. Fully built, verified against real data, running on its own diagnostic page today. The corridor system, our first line of defense against bad routes, is live in production now. This is the layer underneath it, quietly making sure open water actually means open water.