Neighborhoods across Aiken County will be affected differently by these map changes. Some properties will not be affected their risk remains the same. Other properties will be mapped into a higher-risk area and/or show a new base flood elevation. Some properties will be mapped into a lower-risk area than before. Base flood elevation (100-year flood elevation): The height of the base flood or area of land that has a 1 percent chance of flooding in a given year in feet in relation to the North American Vertical Datum of 1988.