New federal maps say New Orleans is much less vulnerable to flooding than it was before Hurricane Katrina struck more than 10 years ago.

As a result, Mayor Mitch Landrieu says, half of the city's properties will see a big drop in their flood insurance costs.

Since Katrina, the Army Corps of Engineers has spent more than $14.6 billion improving the city's defenses against flooding. At a news conference Friday, Landrieu said about 53 percent of the 85,000 insurance policies in the city would see lower rates.

Katrina struck on Aug. 29, 2005, and after levees and floodwalls broke during the storm about 80 percent of New Orleans was flooded. Katrina was the nation's costliest natural disaster.

Since Katrina, the Army Corps of Engineers has spent more than $14.6 billion improving the city's defenses against flooding. The work includes a ring of new levees, floodwalls and floodgates protecting the city from hurricanes. Also, the corps is revamping the city's drainage system.

On March 30, the Federal Emergency Management Agency released new flood-risk maps for New Orleans and they depict many parts of the city as much safer. The new maps replace ones developed in 1984. Developing the maps is a complex undertaking and city officials have pushed hard to get lower rates.

FEMA assesses flood risk nationwide and issues flood maps by which flood insurance rates are set.

Landrieu said a homeowner paying about $960 a year now should see a savings of about $460 when the new maps go into effect in October.

In New Orleans, about 3 percent of the policies in areas on the edge of the city and closer to the Gulf of Mexico will see rate increases, the city said.

In neighborhoods now deemed to be out of risk of flooding, property owners are not federally required to have flood insurance.

Still, Landrieu urged everyone to buy the flood insurance, which is funded through a national program.

"It's cheap enough for everybody to have," Landrieu said.

The risk of flooding remains a danger. New Orleans is a coastal city that's been struck repeatedly by hurricanes over its history.

Also, much of the city lies below sea level and much of the land that once existed between New Orleans and the Gulf of Mexico has disappeared and turned into open water.