Relative darkness of gray tones

• A. Register Marks
• B. Stereoscopic vision
• C. Symbols
• D. Shades

Answer: (D)

Tonal value in grayscale maps is about how the relative darkness of gray tones communicates differences in the depicted variable. The shades—from light to dark—provide a continuous scale that lets you compare areas when color isn’t used or available, conveying changes in density, elevation, or intensity through a grayscale gradient. This is why shades best capture the idea of representing variation with gray tones. Register marks are printing alignment cues, stereoscopic vision is about depth perception from two eyes, and symbols are discrete icons for features; none of these convey the nuanced gradation of darkness that shades do.