Abstract: After FEMA flood maps are scanned and converted to raster maps on a computer system, they are georeferenced. The georeferenced raster maps are stored on the system. Map inset polygons are surrounded by a virtual bounding box and a determination is made whether each grid rectangle intersects any bounding box. For each such intersection, the relevant inset polygon is traced to determine if it actually intersects the grid rectangle. If there is such intersection, the inset polygon is added to a list attached to the grid rectangle. At the end of the process, the list for each grid rectangle identifies each inset polygon intersected thereby. When an address of a property subject to a flood zone determination is entered into the system and geocoded, the grid rectangle containing the address is immediately called up. If only one inset polygon is on the list, it is used to make the flood determination.

Abstract: After FEMA paper flood maps are scanned into a computer system, they are each displayed side-by-side with the relevant portion of a stored vector map covering the geographic area covered by all of the FEMA maps. During display, corresponding points, or “point-pairs,” on each map are marked by a keyboard or mouse device. The corresponding points may be such artifacts as roads, stream beds, railroad tracks, intersections of the foregoing, buildings, mountain peaks, etc., which are identifiable on each displayed map. When two point-pairs are marked, a stored algorithm calculates georeferencing functions which permit translation of the x,y coordinates of the raster map to the latitude,longitude coordinates of the vector map and vice versa. As more point-pairs are marked, the georeferencing functions are refined. Another algorithm removes apparent “bad” points from the georeferencing calculations, which points may re later used if it appears that they are not bad.