Boston is a fenland town. Hull sits at the mouth of an estuary. Both exist in their present shape because centuries of engineering decided the water could be managed rather than avoided, and it still shows in the data.
95% of Boston's housing sits in Environment Agency flood zone 2 or 3. Hull is not far behind, at 92%. The national figure is 8.6%, so across most of England and Wales nine homes in ten sit outside a flood zone entirely. In these two towns very nearly the opposite is true.
Neither figure should surprise anyone who knows the places. It would be stranger if they read any other way. The land under Boston was reclaimed rather than simply built on, drained fen held behind banks and pumps. Hull grew where it did precisely because a tidal estuary made it a working port. The flood map is not revealing anything to either town. It is describing the ground they chose.
What the classification cannot tell you is how those defences are holding, how old the pumps are, or where one particular street sits behind them. That is a local question and a national dataset is the wrong instrument for it.
What it can tell you is that once you set the flood figure aside, Boston and Hull look thoroughly ordinary. Energy scores near the national middle, unremarkable tenure, nothing else flagging. The water is the whole of the story.