Before selling a single report, we ran our method across every parcel touching a FEMA flood zone in nine California counties: 217,236 of them. This page is the summary of what we found, and it is where the numbers on our home page come from.
For each parcel we read the current FEMA flood zone, found the governing Base Flood Elevation where one exists, and measured ground elevations from USGS LiDAR at the building footprint where federal footprint data identified a structure. The screening method is the same one behind the reports we sell; report-level results also carry per-order guards (datum checks, floodway and depth-zone exclusions, geocode-uncertainty disclosure) described in each report's methodology section.
| County | Flood-zone parcels | Mapped outside the SFHA | Candidates ≥1 ft above BFE | Borderline |
|---|---|---|---|---|
| San Mateo County | 36,290 | 23,153 | 1,225 | 744 |
| Santa Clara County | 84,380 | 39,324 | 4,952 | 2,310 |
| Alameda County | 22,502 | 1,225 | 4,701 | 1,494 |
| Contra Costa County | 24,789 | 3,927 | 3,346 | 878 |
| Marin County | 18,888 | 603 | 1,844 | 649 |
| Napa County | 5,743 | 35 | 1,080 | 317 |
| San Francisco | 1,189 | 0 | 87 | 65 |
| Solano County | 10,866 | 16 | 1,537 | 717 |
| Sonoma County | 12,589 | 0 | 2,226 | 492 |
| Total | 217,236 | 68,283 | 20,998 | 7,666 |
"Mapped outside the SFHA" counts parcels touching a flood zone that the current map places outside the high-risk area, many behind accredited levees or removed by map revisions. Candidate counts here use a 1-ft screening bar; the reports we sell hold a stricter 2-ft evidence bar, which about 1 in 16 in-zone parcels' homes cleared in this study.
Two groups of owners are paying more than the map requires: owners already mapped out whose lenders never re-checked, and owners inside the zone whose ground clears the flood elevation. The free lookup on our home page tells you which situation your address is in, from live FEMA records.