🔍 Key Concepts

• NGA charts vs. original foreign charts and how colors may differ from standard U.S. chart symbology • The meaning of a wire-dragged (swept) area on charts and where it is usually explained • Color conventions used for special information or cautionary areas on many chart systems

💭 Think About

• Check Chart No. 1 (or its foreign equivalent) and look at the section dealing with swept areas and wire-drag surveys—what colors are shown there? • Think about which chart colors are typically reserved for highlighting cautionary or supplemental information rather than basic features like buoys or land areas. • Ask yourself: if purple is already being used, which of the remaining colors is most commonly paired with it for similar ‘special-purpose’ or overprinted information on charts?

✅ Before You Answer

• Verify in Chart No. 1 (NGA or Admiralty) how wire-dragged/swept areas are symbolized, including colors. • Confirm which colors on charts are mainly used for overprints and special warnings rather than for normal navigation marks like lateral buoys or land tint. • Eliminate any colors that you know are strongly associated with other fixed meanings (such as land, buoy systems, or traffic separation schemes) on standard charts.