FIGURE 2.5 USGS contour map of Red River. SOURCE: North Dakota State Water Commission.

only 5-foot or 10-foot contour lines (see Figure 2.5). According to regional officials, difficulties in predicting the 1997 flooding demonstrated that maps with greater detail were needed to provide communities in the Red River Valley with better predictions of flood crests. Regional officials considered several different technologies that could be used in developing new maps, including GPS surveying, aerial photography, and lidar. In the end, two areas within the Red River Valley elected to create new contour maps using lidar—because of its speed, accuracy, and cost benefits—in combination with aerial photography. Lidar was also selected because it can provide data for digital elevation models with 1-foot contour intervals, which can be used to reevaluate flood plains in the Red River Valley (see Figure 2.6). Aerial photography was used to identify or verify objects sensed by lidar. For example, trucks, bales of hay, and tractors can be