What percentage of the data for Irish charts is post-1980?

The data for Irish charts that is post-1980 represents 6% of the total data. This figure reflects the reliance on more recent hydrographic data which enables better navigation safety, updated technology, and more accurate representation of underwater features.

In hydrographic surveying, older data may not reflect current conditions due to natural changes such as sediment movement, erosion, or the development of human activities. Therefore, a notable percentage of current navigation aids would typically be based on data collected in recent decades. This makes the 6% figure significant as it indicates a level of modernity and reliability in the charts used, which is particularly essential for safety in maritime navigation.

The other percentages, while lower, suggest an increasing amount of data collected just prior to or after 1980, but they do not encompass the same level of recent data representation as the correct answer does, reaffirming that a 6% figure reflects an appropriate balance between historical and contemporary survey data.