Module 7 - Charts & Publications
Choose a Suitable, Current Chart
An official nautical chart is a special-purpose navigation product issued by, or on the authority of, a hydrographic office or other authorised government institution. It combines coastlines, depths, aids to navigation, hazards, routeing measures and source information, but it is not self-interpreting: the navigator must read its title, notes, symbols, datums, scale and status.
Large-scale charts cover a smaller area with more local detail; small-scale charts cover a wider area with less detail. A 1:20,000 harbour chart is therefore larger scale than a 1:200,000 coastal chart. Use the largest suitable scale for pilotage or a close hazard decision, while retaining the smaller-scale chart needed to understand the wider passage and the approach to the chart boundary.
Scale alone does not make a chart suitable. Check that the coverage includes the intended route and alternatives, the chart is the latest obtainable edition, subsequent applicable corrections are accounted for, the units and horizontal and vertical datums are understood, and cautions or source-quality information do not undermine the planned margin.
| Decision | Check | Why it matters |
|---|---|---|
| Coverage | Route, alternatives and margins lie inside the chart | Avoids navigating at an edge or beyond the product's intended area |
| Scale | Largest suitable scale for the immediate task | Provides the local detail needed without losing wider context |
| Status | Edition and applicable updates | A newly charted danger or changed aid can invalidate an old plan |
| Reference | Units, horizontal datum and Chart Datum | Prevents position, depth and clearance errors |
| Quality | Source or ZOC information and cautions | Sets a realistic margin around uncertain data |
Optional quick check
Section 1 of 5
Which chart is normally the better primary chart for the final approach to a harbour: 1:20,000 or 1:200,000?
Sources and factual review
Continue studying Charts & Publications
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