Recognizing that most of the nation’s flood insurance rate maps were significantly outdated, the Federal Emergency Management Agency embarked on a five-year effort in 2009 to revise them in 12 states.

FEMA paid a national engineering firm, Virginia-based Dewberry, $600 milllion to do the job, public records show.

The maps themselves have two specific pieces of information for each homeowner: elevation and zone.

Elevation refers to the base flood elevation, which determines how high the first livable floor of the house needs to be for the lowest flood risk.

Zone, which includes several categories, refers to whether a building is likely to just flood or also to see damage from waves. Houses in velocity zones must be built to withstand a three-foot wave atop a flood.

Elevation is determined by the height of the land the house is built on compared with the predicted height of the water during a 100-year flood, or a flood that has a 1 percent chance of happening during a given year. Zone, meanwhile, is determined by a detailed engineering analysis that considers proximity to the water, the depth of the water and the location of any structures — such as houses, dunes, bulkheads and fences — that would reduce the energy of a wave coming across the land.

When Hurricane Sandy struck, Dewberry’s engineers already had completed the elevation data. When FEMA officials released the advisory maps, the elevation data included had been all but finalized due to the years of work already completed as part of the remapping effort. The advisory maps, however, did not have a wave analysis study, which determines whether a house is in a velocity zone.

So FEMA’s mappers laid out the worst-case scenario for what the final map would look like, understanding that homeowners and communities could become incensed at what they saw. Velocity zones were more than doubled and included areas that residents and local officials say are highly unlikely to have that type of risk.

FEMA is expected to release another draft of the maps in the coming weeks, to give local and state officials a chance to see what is coming and provide comments, spokesman Darrell Habisch said. By the end of summer, FEMA expects to release preliminary maps to the public, launching the official public review process to make any revisions before the maps are adopted, Habisch said.

“The New Jersey working maps are taking longer to develop than the updated maps for New York because the area of consideration in New Jersey is much larger than in New York, which is confined to NYC and its boroughs,” he said.

State and local officials, many of whom have attended closed-door meetings with the mapping engineers, say they expect the velocity zones will be rolled back in many areas. But no one knows for sure where changes will be made until the maps are released.