Mariners Beware: How Accurate is Your Chart?

“Knowing where things are, and why, is essential to rational decision making.” – Jack Dangermond, Environmental Systems Research Institute (ESRI)

These days, navigators on land and at sea rely on navigational systems to guide them from point A to point B. However, they will only arrive safely if the charts these systems display are accurate. For example, a car’s navigation system may tell drivers looking for a hotel to turn left. Yet, if drivers follow the directions, they might run into men, women, and children entering a mall. When they see a dangerous warning, the drivers assume that the navigation system has malfunctioned, but it has not. It is relying on an out-of-date map that did not include recent construction. The hotel used to be a stand-alone building and back then drivers would turn left to access it. Now a mall encompasses it, and drivers must take a different route to access the entrance. In the ocean, there’s the example of a jack-up barge running aground because the tow master relied on a chart with 150-year-old data. In another example, a vessel lowered its anchor on top of an underwater cable due to reliance on an old chart.

Maps may be inaccurate because the user failed to access the most recent version or because the data fed into the map is inaccurate. Visual cues aid drivers in making informed decisions. Mariners lack this advantage. All they see is water and sky.  For them, accurate charts are crucial for safety at sea. But is the data that goes into the creation of digital charts reliable enough for mariners to place all of their faith in the course set by their navigation system?

Looking at the sources of data that feed the nautical charts electronic navigation systems access is like looking at a Venn diagram. It involves overlapping and intersecting elements, and the mariner must understand this, and the why behind it, in order to navigate his vessel safely. One source of data comes from information collected during hydrographic surveys specifically carried out to acquire data for use in nautical charts. Hydrography measures and describes the features of the ocean that can help mariners avoid groundings and other accidents. For example, mariners need water depth measurements to know how to safely anchor and enter ports that have different water levels.  They also need information about things like shorelines, tides, currents, and underwater obstructions.

Hydrographic offices perform surveys of their waters to collect this type of data for their navigational products. But, hydrographic surveys are resource-intensive and time-consuming. Planning involves meticulous steps, from identifying survey areas to gathering data for execution. Resource constraints hinder frequent surveys. However, the seafloor does not stop changing, causing the demand for the integration of data from various sources to keep maps as current as they can be. Depth information, critical for safe navigation, may come from ship reports, oceanographic measurements, academic or commercial sources, and prior charts. Yet not all data sources are of equal quality. Thus, mariners must realize that they need to scrutinize the origin of data for informed decision-making.

Advancements in survey techniques have revolutionized the industry, and mariners must recognize that newer techniques yield more accurate data than their predecessors. Older data, though once invaluable, may now be outdated, emphasizing the need for continual vigilance.

Chart accuracy is paramount for safe navigation, but it is not infallible. Mariners, like drivers cross-referencing their surroundings, must study the information at hand to ensure they chart the right course.