Regulatory floodplains are extracted from FEMA or provided by consultants to the City. Non regulatory floodplains are provided by consultants, but their accuracy is not guaranteed.FEMA floodplains can either be amended by Letters of Map Revision (LOMR), or Physical Map Revisions (PMR). Historic data between 7/17/1978 and 5/31/2018 rely on PMRs to FIRM Panels; from 5/31/2018 onwards, FEMA exposed a web API that made tracking LOMRs much easier. This is why changes to the floodplain after this date look more "piecemeal" rather than entirely replaced. FEMA Floodplains are automatically updated by a scripted process on a monthly basis.High Hazard Zones are solely recognized by the city as areas which represent the highest risk to loss of life. More information can be found here. These zones are delineated by engineering firms on behalf of the city. They are updated manually by GIS staff.Non-Regulatory Floodplains are updated infrequently.Data: Records with Null INEFFDATEs are the current floodplains.FLOODZONEs beginning with "A" have a 1% chance of flooding (e.g. the 100 Year floodplain)FLOODZONEs equal to "X" are areas with a 0.2% chance of flooding (e.g. the 500 Year floodplain)FLOODZONEs equal to "HHZ" are the High Hazard ZonesFLOODWAYs equal to 1 are Conveyance Zones

Regulatory floodplains are extracted from FEMA or provided by consultants to the City. Non regulatory floodplains are provided by consultants, but their accuracy is not guaranteed.FEMA floodplains can either be amended by Letters of Map Revision (LOMR), or Physical Map Revisions (PMR). Historic data between 7/17/1978 and 5/31/2018 rely on PMRs to FIRM Panels; from 5/31/2018 onwards, FEMA exposed a web API that made tracking LOMRs much easier. This is why changes to the floodplain after this date look more "piecemeal" rather than entirely replaced. FEMA Floodplains are automatically updated by a scripted process on a monthly basis.High Hazard Zones are solely recognized by the city as areas which represent the highest risk to loss of life. More information can be found here. These zones are delineated by engineering firms on behalf of the city. They are updated manually by GIS staff.Non-Regulatory Floodplains are updated infrequently.Data: Records with Null INEFFDATEs are the current floodplains.FLOODZONEs beginning with "A" have a 1% chance of flooding (e.g. the 100 Year floodplain)FLOODZONEs equal to "X" are areas with a 0.2% chance of flooding (e.g. the 500 Year floodplain)FLOODZONEs equal to "HHZ" are the High Hazard ZonesFLOODWAYs equal to 1 are Conveyance Zones