Final answer:
The eight-digit grid coordinates for spot elevation 85 can be determined using the given map of the United States. Locate the grid lines that contain the spot elevation 85 and determine the corresponding digits. Combine these digits to form the eight-digit grid coordinates.
Step-by-step explanation:
The eight-digit grid coordinates for spot elevation 85 can be determined using the given map of the United States. To find the coordinates, first locate the grid lines that contain the spot elevation 85. Then, determine the digit corresponding to the position of spot elevation 85 on each grid line. Combine these digits to form the eight-digit grid coordinates.
For example, on the given map, spot elevation 85 lies between the grid lines -90° and -85° (latitude) and -105° and -100° (longitude). Using interpolation, we can estimate the position of spot elevation 85 to be approximately -87.5° latitude and -102.5° longitude. Therefore, the eight-digit grid coordinates for spot elevation 85 are -87501025.