After two years and more than a billion dollars spent by the Army Corps of Engineers to rebuild New Orleans’s hurricane protection system, that is how much the water level is likely to be reduced if a big 1-in-100 flood hits Leah Pratcher’s Gentilly neighborhood.

Looking over the maps that showed other possible water levels around the city, Ms. Pratcher grew increasingly furious. Her house got four feet of water after Hurricane Katrina, and still stands to get almost as much from a 1-in-100 flood.

By comparison, the wealthier neighborhood to the west, Lakeview, had its flooding risk reduced by nearly five and a half feet.

“If I got my risk reduced by five feet five inches, I’d feel pretty safe,” said Ms. Pratcher, who along with her husband, Henry, warily returned home from Baton Rouge, La. “Six inches is not going to help us out.”

New Orleans was swamped by Hurricane Katrina; now it is awash in data, studied obsessively in homes all over town. And the simple message conveyed by that data is that while parts of the city are substantially safer, others have changed little. New Orleans remains a very risky place to live.