Working with Wisconsin Wetland Inventory Data

Working with FEMA Flood Insurance Rate Maps ArcView Tip Sheet November 27, 2001

Background The Federal Emergency Management Agency (FEMA) is responsible for the administration of the National Flood Insurance Program (42 U.S.C. 4001-4128) and emergency response in the case of natural disasters. To participate in the NFIP, communities must satisfy FEMA's regulations for floodplain management. Through the NFIP, FEMA works with the state and local governments to reduce damages in floodprone areas. Flood hazards are mapped on Flood Insurance Rate Maps (FIRMs) and FEMA has an on-going project to modernize these maps. The Q3 Flood Data product is a digital representation of the 100 year flood boundary on FEMA's FIRM product, intended for use with desktop mapping and GIS technology for planning and emergency reponse. Q3 data do not include floodway boundaries or cross section locations. Digital Q3 Flood Data have been developed by scanning the existing FIRM hardcopy, and vectorizing a thematic overlay of flood risks. Since this process introduces some errors, the Q3 product can not be used in the land use permitting process. Digital Q3 Flood Data are available for 16 counties in Wisconsin. Through the Wisconsin Waters Initiative, the DNR is scanning hard copy FIRMs and geo-referencing these images using the USGS DRGs - creating flood maps in a raster image format. For more information about scanned FIRMs, contact Alan Lulloff by email at [email protected] or by phone at 608-266-2709. In the future FEMA will create and distribute a complete Digital FIRM for each county in Wisconsin. The DFIRMs will contain all of the information on a FIRM image, but in a vector format.

Data Availability Scanned and vector FIRMs are available on the Wisconsin Waters Initiative GIS library in the J:\\wtgislib\fema_tile folder. It is recommended that the Wisconsin Waters Initiative GIS library be mapped as the J drive to your local computer (see the “Mapping the J and K Drive” handout at http://intranet.dnr.state.wi.us/int/water/wm/dsfm/shore/techtraining/documents/arcview2. pdf ). The scanned FIRMs in this library are image files in tiff format. Geo-referenced image files are found in the FEMA_Img folder. Image files that are not geo-referenced are found in the FEMA_ImgNR folder. Image files are stored in folders tiled by county and community. Each image file represents a FEMA map panel. The vector FIRMs are found in the FEMA_Vector folder. There are separate folders for Q3 data and Digital FIRMs. In addition, a shapefile index of all registered FEMA scanned image files can be found in the in Index_Status folder.

Displaying Scanned Flood Insurance Rate Maps Scanned FIRMs may be imported into ArcView and displayed on top of digital raster graphs (scanned USGS topographic maps), or any other data. 1. Import needed digital raster graphs and scanned FIRMs using the Add Theme button with Data Source Types set to Image Data Source. Reorder the themes so that the scanned FIRMs display on top. Notice that the scanned FIRMs obscure the DRGs. 2. To fix this problem, double-click on the theme representing a scanned FIRM to invoke the Legend Editor. Click on the ColorMap button. Double-click on the white box to the right of the 0 character and select the box with the X in it, which is in the upper left corner of the Color Palette. This makes the white color on the scanned FIRM transparent. Double-click on the black box to the right of the 1 character and select a bright red color. Close the Color Palette window and click on the Apply button in the Legend Editor. The scanned FIRM will now display on top of the digital raster graphic (USGS topographic maps).