Final answer:
Base flood elevations are plotted on a topographic or contour map to create a floodplain map.
Step-by-step explanation:
To make a floodplain map, the base flood elevations are plotted on a topographic map or a contour map. A topographic map is a type of map that represents the shape of the Earth's surface with contour lines, which indicate elevations above sea level. By plotting the base flood elevations on a topographic or contour map, it allows for a visual representation of the areas that are at risk of flooding.