ECDIS & Electronic Charts Explained: AVCS vs ARCS vs AIO vs ADC

AVCS, ARCS, AIO, ADC — four Admiralty services, four different jobs. Understanding what each one does, how they interrelate, and what SOLAS actually requires is the foundation of a defensible chart management routine on any vessel running ECDIS.

What is ECDIS?

The Electronic Chart Display and Information System is a type-approved bridge system that satisfies SOLAS chart-carriage requirements when used with official ENCs, kept up to date, and supported by an approved backup arrangement. Unlike a paper chart or a raster image, ECDIS can interrogate chart objects — depths, buoys, traffic separation schemes — trigger safety contour alarms, and display additional overlays such as AIO for passage planning. The combination of object intelligence and official data is what makes it the primary navigation tool on most modern vessels.

ENCs vs RNCs in plain language

ENCs (vector charts) are structured, object-based datasets. Each buoy, depth sounding, and traffic lane is a discrete object with attributes that ECDIS can query, filter, and alarm on. Display adapts intelligently to scale. RNCs (raster charts) are georeferenced images of paper charts — visually familiar, but without object intelligence. ECDIS cannot interrogate an RNC the same way it can an ENC, which is why ENCs are the norm for primary compliance and RNCs are typically used as a supplementary or gap-filling source.

AVCS, ARCS, AIO & ADC: quick comparison

AVCS — Admiralty Vector Chart Service

AVCS is the worldwide portfolio of official ENCs for ECDIS, published by UKHO. It provides global coverage, weekly updates, and full compatibility with the AIO overlay. For most routes and most port state control inspections, AVCS is the default expectation — it delivers compliant, intelligent vector charts that satisfy SOLAS ENCs requirements, support ECDIS alarms, and produce the audit trail that verifiers and inspectors expect to see.

ARCS — Admiralty Raster Chart Service

ARCS delivers official raster versions of Admiralty paper charts — the same content, georeferenced and digitised. It is particularly useful in areas where ENC coverage is not yet complete. Whether ARCS can serve as the primary chart carriage method depends on flag state and port state acceptance; in most jurisdictions ENCs remain the norm, and ARCS serves as a supplementary or transitional source rather than a primary compliance instrument.

AIO — Admiralty Information Overlay

The Admiralty Information Overlay adds Temporary and Preliminary Notices to Mariners, and related planning information, as a transparent layer displayed on top of ENCs in ECDIS or passage planning software. Updated weekly on the same cycle as AVCS, AIO closes a gap that standard ENC data does not address — T&P notices affect navigable water and safety margins but do not appear in the base ENC until they are incorporated permanently. For a bridge team conducting passage planning, an unreviewed AIO layer is an unacceptable risk.

ADC — Admiralty Digital Catalogue

The Admiralty Digital Catalogue is the tool for discovering and managing chart coverage — by route, geographic area, or scale band — across AVCS, ARCS, paper charts, and publications. It is the fastest way to confirm that every cell required for a planned passage is held on permit and current before departure. For fleet managers overseeing coverage across multiple vessels and routes, ADC provides the overview that would otherwise require manual cross-checking of individual permit files.

Compliance corner: SOLAS, updates & backups

• SOLAS carriage is satisfied by: type-approved ECDIS + official ENCs + timely weekly updates + an approved backup arrangement
• Evidence for port state control should include permit files, update logs or reports, and AIO review records — kept together and accessible
• A standardised SOP covering permits → weekly media application → verification → evidence capture removes reliance on individual memory
• Backup arrangements must be approved — a second ECDIS or a portfolio of up-to-date paper charts covering the intended voyage area

S-57/S-63 today — S-100/S-101 tomorrow

Most ENCs in service today are produced in the S-57 format and protected by S-63 licensing and encryption. S-63 governs how cells are encrypted, licensed to specific vessels, and verified at installation — it is the security layer that makes official ENC distribution auditable and tamper-evident.

The next generation is the S-100 framework. Its flagship ENC standard is S-101, designed to interoperate with richer complementary layers: S-102 bathymetric surface data, S-124 navigational warnings, and others. S-100 enables better data fusion on modern ECDIS displays and supports the more granular, object-rich chart presentation that the industry is moving toward. Adoption is underway but incremental — most vessels will run S-57/S-63 for a transitional period alongside emerging S-101 cells.

How weekly updates are delivered

Official services publish updates on a weekly cycle. Updates arrive via the delivery mechanism in use — satellite link, physical media in port, or an automated platform like DIDI Chart. The receiving ECDIS or planning software applies base updates first, then weekly increments. AIO updates on the same rhythm. The SOP should run: permit verification → apply updates → confirm cell status in ECDIS → save the exported report or timestamped screenshot as evidence. The evidence step is the one most commonly skipped, and the one inspectors most commonly ask for.

Quick checklist: from permit to proof

• Import or renew permits for all voyage cells — re-request any that failed
• Apply base and weekly updates from the latest media; re-run if any files were skipped
• Verify status in ECDIS: open the cell report and confirm all cells show as Current
• Check AIO date — confirm the overlay is on the current weekly edition
• Save evidence — export the update report or take a timestamped screenshot to a dedicated Chart Updates folder
• Re-check the route — scan AIO along the planned track for new T&P restrictions, depth changes, or buoyage amendments

Frequently asked questions