Module 19 - Electronic Navigation
Electronic Charts
What you will learn
Distinguish ENC, RNC and leisure-chart data, verify chart status and explain why display appearance alone does not establish official status or safe portrayal.
Electronic chart labels describe data and system status, not simply whether a display looks vector-like or resembles paper. The navigator must know what data are loaded, how they are updated and how the fitted system portrays them.
An Electronic Navigational Chart is official vector data produced to IHO standards for use in a type-approved ECDIS. A Raster Navigational Chart is official raster data for the relevant approved mode. A leisure plotter or app may use useful vector or raster-style data without being an ENC, RNC or an approved ECDIS installation.
For most leisure craft, the RYA currently identifies paper charts as the viable official chart source because an approved digital system suitable for most small craft is not yet available. That boundary does not make plotters unhelpful; it means the navigator must not infer official status, coverage, update quality or legal carriage equivalence from the look of the display.
Vector portrayal depends on scale, layers, safety settings, object attributes and software. Raster portrayal preserves the source image but has different query, alarm and scale behaviour. In either case, verify edition or update status, coverage, datum, source scale, display warnings and the limitations of the fitted equipment.
| Term | What it means | Do not assume |
|---|---|---|
| ENC | Official vector data for type-approved ECDIS use | Every vector plotter chart is an ENC |
| RNC | Official raster chart data for the relevant approved mode | Every scanned chart image is an RNC |
| Leisure chart database | Provider-specific data for a plotter or app | Official status, approval or update equivalence |
Identify what chart data are actually aboard
A charter plotter displays smooth vector symbols and an update date, so a crew member describes it as an official ENC replacement for paper charts.
1. Name the system
Identify the equipment, chart provider, product and whether it is a type-approved ECDIS installation.
2. Name the data
Distinguish official ENC/RNC from private or leisure chart databases.
3. Verify status
Check coverage, update method, licence, source scale, datum and display warnings.
4. State the boundary
Treat the fitted small-craft system according to its actual approval and official-chart status, not its appearance.
Sense check: A vector display is not automatically an ENC, and an ENC is not merely any electronic chart drawn with selectable layers.
Common mistake or limitation
- Calling every vector chart an ENC obscures the official-data and approved-system distinction.
- An update timestamp does not prove complete coverage, correct installation or current navigational warnings.
- Raster and vector products have different behaviour; neither should be judged only by visual familiarity.
- ECDIS carriage and backup rules for SOLAS ships should not be mechanically transferred to a leisure plotter.
Recap
- ENC and RNC are official data terms tied to approved navigation-system use.
- Most leisure plotter data are not automatically official ENC replacements.
- Verify coverage, update, datum, source scale and portrayal behaviour.
- Use the fitted system within its documented status and limitations.
Optional quick check
Section 4 of 18
Which statement is defensible for a typical leisure plotter?
Sources and factual review
Reviewed 20 August 2026 - Compass Revision editorial review.
Continue studying Electronic Navigation
This public lesson is part of Revision Module 19. Full revision access adds the guided Learn, Practise and Test flow, flashcards and revision progress.