Which statement is true regarding the age of data used for current Irish hydrographic charts?

The assertion that most data used for current Irish hydrographic charts is over 100 years old reflects the reality that certain areas may still rely on historical data collected long ago, especially in regions where surveys have not been frequently updated. Hydrographic surveying data can vary significantly based on location, and many nautical charts have historical layers that remain in use due to the lack of recent survey activity. Some chart data might also be derived from initial surveys conducted in the 19th and early 20th centuries, which were the foundation of contemporary nautical charts. While advancements in technology and methodology have improved data collection, there may still be substantial historical information embedded in the current charts.

In contrast, while ongoing yearly surveys do contribute to the data used in updating hydrographic charts, the emphasis on the historical nature of information indicates that, for many areas, reliance on over a century-old data still persists.