Making a nautical chart is like doing a jigsaw puzzle whose pieces may or may not be in the box. When the information a chart needs already exists, cartographers can assemble one relatively fast. When pieces are missing or out of date, someone has to go out and collect them first — and that is what turns months into years.
NOAA's Office of Coast Survey produces nautical charts for U.S. coastal waters, including the Great Lakes and U.S. territories. Credit: NOAA.
What goes into a chart
A nautical chart exists for one purpose: to give ships what they need to navigate safely. That takes several kinds of information:
- Natural features — the depth of the water, the shape of the shoreline, and the locations of rocks and other dangers.
- Man-made structures — the position and characteristics of things like bridges and cables that pass over navigable rivers, and the boundaries and depths of dredged channels.
- Aids to navigation — the positions and descriptions of buoys, beacons and lights, a set of features that other maps rarely show.
Where the pieces come from
For a new chart, some of this information is usually on hand already. When it is missing or too old, NOAA collects new data from a range of providers:
| Provider | What it supplies |
|---|---|
| NOAA's hydrographic survey ships and planes | water depth and shoreline |
| U.S. Army Corps of Engineers | the limits and depths of ship channels |
| U.S. Coast Guard | aids to navigation |
Many other organizations contribute as well.
Six months, or several years
Compiling the data can take as little as six months. But if new hydrographic or topographic surveys are needed, scheduling, collecting and processing them can stretch the job to several years. How long depends on where the chart is, how much surveying it needs, and what other charts are competing for the same resources.
A chart is never finished
Once a new chart exists, the work has only begun, because keeping it current never ends. Shorelines change, seafloors shift, silt builds up, submerged dangers are discovered and buoys are moved — and each of those changes has to reach the chart.
Sources
Based on "How long does it take to produce a nautical chart?" from NOAA's National Ocean Service, a work of the United States government in the public domain.
Licence: CC0 1.0 (public domain) · Adapted from oceanservice.noaa.gov
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