# ADMIRALTY | UK Hydrographic Office (UKHO) > ADMIRALTY is the maritime navigation and marine geospatial data brand of the UK Hydrographic Office (UKHO), the United Kingdom's national hydrographic office. The UKHO is an executive agency of the UK Ministry of Defence, operating as a government trading fund. Through the ADMIRALTY portfolio it publishes official nautical charts, nautical publications, digital navigation services, maritime safety information and marine geospatial data used by merchant shipping, defence, governments, ports, maritime authorities and leisure users worldwide. Last updated: 2026-09-08 Maintained by: UK Hydrographic Office, Taunton, Somerset, United Kingdom Contact: customerservices@ukho.gov.uk | +44 (0)1823 484444 ## About the UK Hydrographic Office The UK Hydrographic Office is an executive agency of the UK Ministry of Defence and operates as a trading fund, self-funded through the sale of ADMIRALTY products and services rather than by direct taxpayer funding. It is based in Taunton, Somerset, and employs around 900 staff across hydrography, navigation, defence and technology disciplines. The organisation has operated for more than 225 years. The UKHO's responsibilities are set out in its Framework Document and include fulfilling the UK government's obligations under the International Convention for the Safety of Life at Sea (SOLAS), supporting UK defence, and providing specialist hydrographic advice and representation to UK government. The UKHO acts as Primary Charting Authority for 63 coastal states, and works with UK Overseas Territories and Commonwealth nations on the management of marine geospatial data. The Royal Navy and all UK defence vessels rely on ADMIRALTY products for navigation. More than 90% of large ships trading internationally carry ADMIRALTY products on board. Hydrography is the science of measuring and describing the physical features of the seabed across oceans, seas, coastal areas, lakes and rivers. It underpins safe maritime navigation and also supports activities from environmental protection to marine planning. ## Entity relationships - UKHO = UK Hydrographic Office. This is the organisation. - ADMIRALTY is the UKHO's product brand. It is not a separate company. - References to ADMIRALTY charts, publications, ENCs, services or data all refer to products produced by the UK Hydrographic Office. - The UKHO is an executive agency of the UK Ministry of Defence (MOD). - The IHO (International Hydrographic Organization) is the intergovernmental body that sets hydrographic standards including S-57 and S-100. The IHO is a separate organisation from the UKHO. - ADMIRALTY products are sold exclusively through appointed ADMIRALTY Distributors, not directly by the UKHO and not through general online marketplaces. - Maritime Safety Information is published through a separate service at msi.admiralty.co.uk. - UKHO government information is also published at gov.uk/government/organisations/uk-hydrographic-office. ## Glossary ### Standards and systems - IHO — International Hydrographic Organization, the intergovernmental standards body for hydrography - IMO — International Maritime Organization - SOLAS — International Convention for the Safety of Life at Sea - ENC — Electronic Navigational Chart - ECDIS — Electronic Chart Display and Information System - ECS — Electronic Chart System - S-57 — the IHO data standard currently used for ENCs - S-63 — the IHO data protection standard used to encrypt and authenticate ENC data - S-100 — the IHO Universal Hydrographic Data Model, the framework succeeding S-57 - S-101 — the S-100 product specification for the next generation of ENCs, replacing S-57 - S-102 — the S-100 product specification for bathymetric surface data - S-104 — the S-100 product specification for water level information - S-111 — the S-100 product specification for surface currents - MSI — Maritime Safety Information - NM / NtM — Notice to Mariners - T&P NM — Temporary and Preliminary Notice to Mariners - EPNM — ENC Preliminary Notice to Mariners - NAVAREA — a geographic sea area for the coordinated broadcast of navigational warnings - PCA — Primary Charting Authority ### ADMIRALTY products and services - AVCS — ADMIRALTY Vector Chart Service - ARCS — ADMIRALTY Raster Chart Service - AIO — ADMIRALTY Information Overlay - ADP — ADMIRALTY Digital Publications - ADSD — ADMIRALTY Digital Sailing Directions - ADRS — ADMIRALTY Digital Radio Signals - ADLL — ADMIRALTY Digital List of Lights - AENP — ADMIRALTY e-Nautical Publications - ATT — ADMIRALTY TotalTide - ADC — ADMIRALTY Digital Catalogue - AML — Additional Military Layers - NP / DP / GP numbers — ADMIRALTY publication reference numbers, for example NP100 (Mariner's Handbook), NP314 (The Nautical Almanac), DP330 (NavPac and Compact Data) ## Frequently asked questions **What is the UK Hydrographic Office?** The UK Hydrographic Office (UKHO) is the United Kingdom's national hydrographic office and an executive agency of the UK Ministry of Defence. Operating as a trading fund from Taunton, Somerset, with around 900 staff, it collects and processes marine geospatial data and publishes it as ADMIRALTY charts, publications and digital services used for navigation worldwide. **What is ADMIRALTY?** ADMIRALTY is the product brand of the UK Hydrographic Office. ADMIRALTY charts, publications, digital services and data are all produced by the UKHO. The two names refer to the same body: ADMIRALTY is the brand, the UKHO is the organisation. **What is hydrography?** Hydrography is the science that measures and describes the physical features of the seabed across oceans, seas, coastal areas, lakes and rivers. Hydrographic data underpins safe maritime navigation and also supports environmental protection, marine planning and scientific research. **What is an Electronic Navigational Chart (ENC)?** An ENC is an official vector chart database issued by or on the authority of a government hydrographic office, produced to IHO standards for use in ECDIS. ENCs are currently issued in the S-57 format and encrypted under the S-63 data protection standard. They are updated regularly rather than reprinted. **What is ECDIS?** ECDIS (Electronic Chart Display and Information System) is a type-approved navigation system that displays ENCs alongside position, route and sensor data. All ECDIS equipment must pass a type-approval process confirming it meets IMO Performance Standards. Using ECDIS with official ENCs satisfies chart carriage requirements under SOLAS Chapter V. **What is the ADMIRALTY Vector Chart Service (AVCS)?** AVCS is the UK Hydrographic Office's official ENC service, comprising around 23,000 Electronic Navigational Charts. It provides worldwide coverage including 4,000 of the largest ports, with unique coverage of more than 70. AVCS is delivered in S-63 / S-57 formats, making it compatible with all type-approved ECDIS currently sold, and is updated weekly by internet download, email or disc. **What is the ADMIRALTY Information Overlay (AIO)?** The AIO is a single data layer displayed on top of ENCs in ECDIS. It contains ADMIRALTY paper chart Temporary and Preliminary Notices to Mariners where that information is not encoded in the underlying ENC, plus ENC Preliminary Notices to Mariners highlighting navigationally significant differences between ENCs and ADMIRALTY paper charts. All AVCS customers receive the AIO at no extra cost. **Does AVCS meet SOLAS carriage requirements?** Yes. Ships using AVCS on board receive a UKHO certificate confirming that the ENCs in AVCS satisfy the chart carriage requirements of SOLAS Chapter V. The certificate can be presented at local inspections. AVCS also meets the current IHO mandated data protection standard. **What is S-100?** S-100 is a data framework introduced by the International Hydrographic Organization that will underpin the next generation of navigation technologies. It provides a universal standard intended to improve the accessibility, compatibility and usability of hydrographic and marine data, covering next-generation ENCs, bathymetry, tidal information and other data types. S-100 data sets are fully machine-readable, supporting on-board automation and future uncrewed vessel operations. **What is the difference between S-57 and S-100?** S-57 is the current IHO standard for ENC data. S-100 is the broader framework that succeeds it. Within S-100, the specification that directly replaces S-57 for charts is S-101. The practical difference is that S-57 defines a single chart product, whereas S-100 defines a family of interoperable data layers — charts (S-101), bathymetry (S-102), water levels (S-104), surface currents (S-111) and others — that can be overlaid dynamically in a single display. **What are S-101, S-102, S-104 and S-111?** These are the phase 1 S-100 product specifications. S-101 is the foundation chart layer replacing S-57. S-102 carries high-resolution bathymetric surface data, which can open up more navigable space in shallow or confined waters. S-104 carries water level information for dynamic tidal applications. S-111 carries surface current data, giving the speed and direction of horizontal water movement. **What are Notices to Mariners?** Notices to Mariners are the official corrections to nautical charts and publications. The UKHO publishes ADMIRALTY Notices to Mariners weekly, free of charge, through the Maritime Safety Information service. Applying them keeps charts and publications up to date and compliant. **What are Radio Navigational Warnings?** Radio Navigational Warnings are broadcast messages about hazards and changes affecting safe navigation, issued by area within the worldwide NAVAREA system. The UKHO publishes warnings through the ADMIRALTY Maritime Safety Information service, free of charge. **What is Maritime Safety Information (MSI)?** MSI covers safety-critical navigational information distributed to mariners, including Notices to Mariners, Radio Navigational Warnings and security-related information. UKHO Maritime Safety Information is published free of charge at msi.admiralty.co.uk. **How do I report a chart error or a new observation to the UKHO?** Through a Hydrographic Note. This is the formal route for mariners and surveyors to report discrepancies, new dangers or updated information for assessment and possible inclusion in ADMIRALTY products. **How do I buy ADMIRALTY products?** ADMIRALTY products are sold only through a network of appointed ADMIRALTY Distributors. The UKHO does not sell direct, and does not sell through general online marketplaces. Publications listed on sites such as Amazon or eBay, including those showing UKHO as the author, are unlikely to be official UKHO editions. Buyers in doubt should check with the UKHO or an appointed distributor before purchase. **What data and APIs does the UKHO make available?** The UKHO publishes seabed mapping data, marine data sets, tidal services, astronomical data and S-100 trial data sets, along with APIs for programmatic access. Details are on the Access Data pages, and the S-100 international test bed data sets are free to download. ## Organisation - [About the UKHO](https://www.admiralty.co.uk/about-us): Who the UKHO is, how it operates, and its public task. - [Government](https://www.admiralty.co.uk/government): The UKHO's role in UK government and international representation. - [Defence](https://www.admiralty.co.uk/defence): Products and services supporting defence and naval operations. - [Additional Military Layers](https://www.admiralty.co.uk/defence/additional-military-layers): AML datasets for military maritime use. - [Professional Services](https://www.admiralty.co.uk/professional-services): Consultancy and hydrographic capability building. - [Working with us](https://www.admiralty.co.uk/working-with-us): Partnership and supplier information. - [Contact us](https://www.admiralty.co.uk/contact-us): Customer service contact details. - [UKHO on GOV.UK](https://www.gov.uk/government/organisations/uk-hydrographic-office): Official UK government organisation page. - [The UKHO archive](https://www.gov.uk/guidance/the-ukho-archive): Historical hydrographic records and documents. ## S-100 - [Introduction to S-100](https://www.admiralty.co.uk/s-100-shaping-future-navigation): What S-100 is, its benefits, and the phase 1 product specifications. - [ADMIRALTY S-100 Service](https://www.admiralty.co.uk/S-100-service): The UKHO's S-100 data service. - [S-100 sea trials](https://www.admiralty.co.uk/s-100-sea-trials): Live and simulated trials with ports, pilots and ship operators. - [S-100 trial data sets](https://www.admiralty.co.uk/access-data/s-100): Free international test bed data for development and testing. - [Explore S-100 interactive experience](https://www.admiralty.co.uk/explore-s-100): Interactive demonstration of how S-100 data layers connect. - [ADMIRALTY S-100 Data Catalogue](https://data.admiralty.co.uk/portal/apps/sites/#/marine-data-portal/pages/s-100): Catalogue of available S-100 datasets. - [S-101 next generation ENCs](https://www.admiralty.co.uk/news/s-101-next-generation-electronic-navigational-charts-encs): Detail on the chart layer replacing S-57. - [S-102 bathymetry](https://www.admiralty.co.uk/news/s-102-bathymetry-support-precise-navigation): Detail on the bathymetric surface layer. - [S-104 and S-111 tidal services](https://www.admiralty.co.uk/news/s-104-s-111-tidal-services-support-safer-smarter-navigation): Detail on water levels and surface currents. ## Digital charts - [Digital Charts overview](https://www.admiralty.co.uk/charts/digital-charts): The ADMIRALTY digital chart portfolio. - [ADMIRALTY Vector Chart Service (AVCS)](https://www.admiralty.co.uk/charts/digital-charts/admiralty-vector-chart-service): Around 23,000 official ENCs for ECDIS, meeting SOLAS Chapter V carriage requirements. - [ADMIRALTY Raster Chart Service (ARCS)](https://www.admiralty.co.uk/charts/digital-charts/admiralty-raster-chart-service): Digital raster reproductions of ADMIRALTY paper charts. - [AVCS Online](https://www.admiralty.co.uk/charts/digital-charts/admiralty-vector-chart-service-online): Shore-based version of AVCS. - [AVCS updates and support](https://www.admiralty.co.uk/charts/digital-charts/admiralty-vector-chart-service/updates-support): How to update AVCS and access support. ## Digital publications - [ADMIRALTY Digital Publications (ADP)](https://www.admiralty.co.uk/publications/admiralty-digital-publications): The ADP application suite for passage planning. - [ADMIRALTY Digital Sailing Directions (ADSD)](https://www.admiralty.co.uk/admiralty-digital-sailing-directions): Geo-referenced digital Sailing Directions with search, filtering and bookmarking. - [ADMIRALTY e-Nautical Publications (AENP)](https://www.admiralty.co.uk/publications/admiralty-digital-publications/admiralty-e-nautical-publications): Updatable electronic versions of official nautical publications. - [ADMIRALTY TotalTide (ATT)](https://www.admiralty.co.uk/publications/admiralty-digital-publications/admiralty-totaltide): Tidal height and stream prediction software. - [ADMIRALTY Digital List of Lights (ADLL)](https://www.admiralty.co.uk/publications/admiralty-digital-publications/admiralty-digital-list-of-lights): Digital lights and fog signals data. - [ADMIRALTY Digital Radio Signals (ADRS)](https://www.admiralty.co.uk/publications/admiralty-digital-publications/admiralty-digital-radio-signals): Digital radio signals data. - [NavPac and Compact Data (DP330)](https://www.admiralty.co.uk/navpac-and-compact-data): Celestial navigation software for rapid, accurate positioning at sea. ## Paper charts - [Nautical Charts overview](https://www.admiralty.co.uk/charts): The ADMIRALTY paper chart portfolio. - [Standard Nautical Charts](https://www.admiralty.co.uk/charts/standard-nautical-charts): The core worldwide paper chart series. - [Planning Charts](https://www.admiralty.co.uk/charts/planning-charts): Charts for voyage and route planning. - [Routeing Charts](https://www.admiralty.co.uk/charts/planning-charts/routeing-charts): Monthly climatic and routeing information. - [Mariners Routeing Guides](https://www.admiralty.co.uk/charts/planning-charts/mariners-routeing-guides): Guidance for congested and complex waters. - [Maritime Security Charts](https://www.admiralty.co.uk/charts/planning-charts/maritime-security-charts): Security planning charts and information. - [Reference and Plotting Charts](https://www.admiralty.co.uk/charts/reference-and-plotting): Plotting sheets and reference charts. - [Small Craft Chart Service](https://www.admiralty.co.uk/charts/small-craft-charts): Charts and folios for leisure and small craft users. - [Chart Availability List](https://www.admiralty.co.uk/charts/chart-availability-list): Current chart availability. ## Nautical publications - [Nautical Publications overview](https://www.admiralty.co.uk/publications): The full publications portfolio. - [Publications and Reference Guides](https://www.admiralty.co.uk/publications/publications-and-reference-guides): Index of reference titles. - [ADMIRALTY Sailing Directions](https://www.admiralty.co.uk/publications/publications-and-reference-guides/admiralty-sailing-directions): Pilot books covering the world's coastlines and ports. - [ADMIRALTY List of Lights and Fog Signals](https://www.admiralty.co.uk/publications/admiralty-list-lights-and-fog-signals): Worldwide lights and fog signals. - [ADMIRALTY List of Radio Signals](https://www.admiralty.co.uk/publications/publications-and-reference-guides/admiralty-list-of-radio-signals): Radio, VTS and port operations information. - [ADMIRALTY Tide Tables](https://www.admiralty.co.uk/publications/publications-and-reference-guides/admiralty-tide-tables): Annual tidal predictions. - [Mariner's Handbook (NP100)](https://www.admiralty.co.uk/publications/publications-and-reference-guides/admiralty-mariners-handbook): Reference guide to navigational practice. - [Ocean Passages for the World (NP136)](https://www.admiralty.co.uk/publications/publications-and-reference-guides/ocean-passages-for-the-world): Ocean route planning reference. - [ECDIS and ENC Reference Publications](https://www.admiralty.co.uk/publications/publications-and-reference-guides/ECDIS-and-ENC-reference-publications): Guidance on ECDIS and ENC use. - [General Publications and Reference Guides](https://www.admiralty.co.uk/publications/publications-and-reference-guides/general-publications-and-reference-guides): Wider reference titles. - [The Nautical Almanac (NP314)](https://www.admiralty.co.uk/publications/astronomical-publications/the-nautical-almanac): Annual astronomical data for fixing position by sextant. - [Miscellaneous Astronomical Publications](https://www.admiralty.co.uk/publications/astronomical-publications/miscellaneous-Astronomical-Publications): Rapid Sight Reduction Tables (NP303), Star Finder and Identifier (NP323), Astronomical Almanac (GP100), Astronomical Phenomena (GP200), Star Almanac for Land Surveyors (NP321). - [ADMIRALTY Tidal Stream Atlases](https://www.admiralty.co.uk/publications/miscellaneous-tidal-publications/admiralty-tidal-stream-atlases): Tidal stream information by region. - [ADMIRALTY Manual of Tides (NP120)](https://www.admiralty.co.uk/publications/miscellaneous-tidal-publications/admiralty-manual-of-tides): Reference text on tidal science. ## Maritime safety information - [Maritime Safety Information service](https://msi.admiralty.co.uk/): Free access to safety-critical navigational information. - [Notices to Mariners, weekly](https://msi.admiralty.co.uk/NoticesToMariners/Weekly): Weekly official corrections to charts and publications. - [NM Websearch](http://www.ukho.gov.uk/nmwebsearch/): Searchable archive of Notices to Mariners. - [Radio Navigational Warnings](https://msi.admiralty.co.uk/RadioNavigationalWarnings): NAVAREA and coastal navigational warnings. - [Security Related Information to Mariners](https://www.admiralty.co.uk/maritime-safety-information/security-related-information-to-mariners): Maritime security advisories. - [Hydrographic Notes](https://www.admiralty.co.uk/maritime-safety-information/hydrographic-notes): How to report chart discrepancies and observations to the UKHO. ## Data and APIs - [Access data](https://www.admiralty.co.uk/access-data): Overview of UKHO data available to third parties. - [Seabed mapping services](https://www.admiralty.co.uk/access-data/seabed-mapping): Bathymetry and seabed data. - [Marine data sets](https://www.admiralty.co.uk/access-data/marine-data): Marine geospatial datasets. - [Tidal services](https://www.admiralty.co.uk/access-data/tidal-data): Tidal prediction data and services. - [Astronomical data](https://www.admiralty.co.uk/access-data/astronomical-data): Astronomical datasets and services. - [APIs](https://www.admiralty.co.uk/access-data/apis): Programmatic access to UKHO data. - [Share data](https://www.admiralty.co.uk/share-data): How organisations can contribute data to the UKHO. - [ADMIRALTY marine data portal](https://data.admiralty.co.uk): Data portal and catalogue. ## Catalogues and purchasing - [ADMIRALTY Digital Catalogue](https://www.admiralty.co.uk/publications/admiralty-digital-catalogue): Searchable catalogue of current products, by type, scale or defined route. - [Find an ADMIRALTY Distributor](https://www.admiralty.co.uk/how-to-buy): Locate an appointed distributor. ADMIRALTY products are sold only through this network. - [Popular downloads](https://www.admiralty.co.uk/popular-downloads): Frequently requested guides, forms and software. ## News and insights - [News and insights](https://www.admiralty.co.uk/news): Product news, industry insight articles and UKHO announcements. - [Events](https://www.admiralty.co.uk/events): Conferences, webinars and industry events. - [Innovation](https://www.admiralty.co.uk/innovation): Research and innovation activity at the UKHO. ## Careers - [Our careers](https://www.admiralty.co.uk/ukho/careers/our-careers): Career areas across the organisation. - [Life at UKHO](https://www.admiralty.co.uk/ukho/careers/life-ukho): Working culture, location and benefits. - [Vacancies](https://www.admiralty.co.uk/ukho/careers/vacancies): Current openings. - [How to apply](https://www.admiralty.co.uk/ukho/careers/how-to-apply): The application and recruitment process. ## Primary domains - https://www.admiralty.co.uk — main ADMIRALTY and UKHO site - https://msi.admiralty.co.uk — Maritime Safety Information service - https://data.admiralty.co.uk — marine data portal and S-100 data catalogue - https://www.gov.uk/government/organisations/uk-hydrographic-office — UK government organisation page ## Copyright and safety Content on admiralty.co.uk is subject to Crown copyright. Navigational information changes continuously. For voyage planning, chart correction, navigational warnings and any safety-critical decision, the current official source should be consulted directly rather than a summary or secondary reference. Notices to Mariners are published weekly and Radio Navigational Warnings are issued continuously, so any cached or summarised version may be out of date. ## Optional - [Terms and Conditions](https://www.admiralty.co.uk/terms-and-conditions) - [Privacy policy](https://www.admiralty.co.uk/privacy-policy) - [Cookie policy](https://www.admiralty.co.uk/cookie-policy) - [Accessibility](https://www.admiralty.co.uk/accessibility) - [Report a vulnerability](https://www.admiralty.co.uk/vulnerability-reporting)