How FEMA flood zones work in a ZIP comparison

A flood bar on a ZIP report is the share of that ZIP mapped into broad hazard groups. It is not a determination for a house, a mortgage, or an insurance quote.

Updated September 29, 2026

What the map is

FEMA publishes flood hazard maps used for the National Flood Insurance Program. The National Flood Hazard Layer is the digital version of those maps. The best-known category is the Special Flood Hazard Area, often described as the area with a 1 percent annual chance of flooding, sometimes called the 100-year floodplain. That phrase does not mean a flood happens once a century. It means the mapped annual chance is about 1 in 100. Over a 30-year mortgage, that chance adds up.

Other mapped areas include moderate hazard, minimal hazard, and areas affected by levees. A levee zone is not the same thing as “no flood hazard.” It means the map is accounting for a flood-control structure, which has its own conditions and failure risk.

What the report bar shows

Consilium Compare turns the overlap between a ZIP and those mapped zones into one segmented bar. Each color is a share of the ZIP. Shares that are zero are left off so the bar stays one line, not a stack of separate pills. The bar is there so you can see whether flood-mapped land is a large part of one ZIP and a small part of the other.

The share is of the ZIP, not of a neighborhood you have already chosen inside it, and not of a parcel. A ZIP can be mostly minimal hazard and still contain a block in a Special Flood Hazard Area. The reverse is also true.

What it does not decide

A ZIP overlap does not tell you the base flood elevation at a door, whether a structure is elevated, whether a lender will require flood insurance, or what a policy will cost. Maps are revised. A property can be newly included or removed. Local drainage, fill, and building changes are not in a ZIP share.

Use the bar to see whether flood-mapped land is a meaningful difference between the two ZIPs. Before you rely on it for a purchase, look up the address on the current FEMA flood map and ask the insurer and, if you have one, the surveyor or local floodplain office.

The comparison still does not pick a ZIP. Less mapped flood hazard is one fact among others. See it in the sample report, next to the notes on industrial releases and air monitors.