What percentage of charts published of Irish waters is based on data that is more than 100 years old?

The correct choice indicates that 60% of charts published for Irish waters are based on data that is over a century old. This reflects the historical context of hydrographic surveying in Ireland, where certain areas were extensively surveyed in the late 19th and early 20th centuries. Such longstanding data often forms the basis of contemporary nautical charts, especially in regions where more recent surveys have not been conducted or updated.

The reliance on historical data is not uncommon in hydrographic surveying, particularly for countries with extensive maritime histories like Ireland. The percentage of 60% signifies a significant portion, suggesting that modernization and reevaluation of these charts are essential for ensuring navigational safety, environmental management, and the updating of maritime infrastructure.

Regular updates and modern surveying methods, including the use of advanced technology such as satellite positioning and sonar, are critical for producing accurate and up-to-date nautical charts. This highlights the importance of ongoing hydrographic surveys and the need for authorities to address outdated information effectively.