Admiralty Information Overlay

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The AIO is a worldwide digital dataset that is designed to be displayed over ENCs in ECDIS and other chart display systems to provide additional information during passage planning. The AIO is refreshed every week, as part of the AVCS Weekly Update and is issued on disc and by download. The weekly disc contains the base edition and all the updates, so you only need to load the most recent disc on board. Some back of bridge software applications allow the vessel to download the updates each week. The AIO is a single large dataset, so you should work with your ADMIRALTY Chart Agent if you wish to avoid large download sizes by using a disc when you load your ECDIS for the first time or when a New Edition is released. In common with all ENCs, downloaded weekly updates can only be applied to the most recent base edition issued, and must be applied in sequence. Where the ENCs do not include temporary information, the Overlay contains ADMIRALTY Temporary & Preliminary Notices to Mariners (T&P NMs) that are issued for paper charts. Each polygon carries the same number as the original NM in the ADMIRALTY Weekly Bulletin. The AIO also draws attention to areas where differences between ENCs and paper charts may affect the passage plan.


Except for areas where there is no ADMIRALTY chart at equivalent scale to the ENC (indicated by ‘No Overlay’ polygons), AIO covers the whole world. Temporary information is assessed for inclusion as follows:

  • Excluded if the producer nation confirms that they include temporary information in their ENCs.
  • Included if it affects an ADMIRALTY paper chart and has been issued as a T&P NM.
  • Excluded if the information only relates to paper charts and is therefore not relevant to the ECDIS user.
  • Included as EPNM if the information is about a navigationally significant difference between the ENC and the equivalent paper chart.


The Overlay can be displayed on AIO compatible ECDIS equipment as well as some software applications. Please see the UKHO website for a list of AIO-compatible ECDIS, or consult your supplier. The Overlay data is held on a single CD which is installed and updated in the same way as ENCs. The AIO permit GB800001 is free of charge for AVCS users and can be added to your licence. Please contact your ADMIRALTY Chart Agent if you wish to use the Overlay or cannot view it on your ECDIS.

Managing T&P NMs with AIO


The UKHO issues a weekly bulletin of Temporary and Preliminary Notices to Mariners (T&P NMs) which contains temporary information of navigational interest to mariners using ADMIRALTY paper charts. Mariners are only required to hold Notices to Mariners for paper charts that are on board. Like UKHO, Hydrographic Offices around the world issue Notices to Mariners to update their paper charts. Some countries do not issue T&P NMs and some do not update their ENCs with temporary information. If the producer nation does not include temporary information in their ENCs but the UKHO has issued a T&P NM for an equivalent scale paper chart, it is added to the ADMIRALTY Information Overlay (AIO). This allows you to receive extra temporary information which has not been included in your subscribed ENCs.

The T&P NMs are displayed as polygons over the ENCs on the ECDIS.


The full text of the NM is included as an associated text file which can be displayed by selecting the ‘Temporary Notice to Mariners’ or ‘Preliminary Notice to Mariners’ feature in the ECDIS Pick Report. Any associated diagrams can also be viewed through the Pick Report.


AIO does not contain paper T&P NMs issued by the ENC producer.

There may be a time delay between the publication or cancellation of national T&P NMs and the publication or removal of the equivalent ADMIRALTY T&P NMs that are included in AIO.

Although UKHO tries to avoid duplication, it is possible that the AIO will occasionally contain T&P information similar to that displayed in the ENC. AIO does not include T&P NMs that only relate to paper charts. For instance, a nontemporary update to a local ENC may result in a T&P NM for the ADMIRALTY paper chart. Because the information is contained in the ENC, the ADMIRALTY T&P NM would be excluded from AIO. Some ADMIRALTY T&P NMs solely refer to non-navigational charts e.g. Port Approach Guides and Maritime Security Charts. As the T&P NM often relates to text boxes and cannot be geo-displayed, they are not included in AIO. A list of ENC producers whose policy is to include T&P NM information in their ENCs can be found at and in the INFO folder on all AVCS and AIO discs. Please note that official ENCs remain the primary source of information for navigation at all times.


ENC Preliminary (EP) NMs highlight navigationally significant differences between ENCs and ADMIRALTY paper charts. These NMs are displayed in the same way as T&P NMs, as a polygon with a hatched fill which indicates the area affected by the NM. Each NM is allocated a unique EP NM number and is exclusive to AIO.


The full text of the NM can be viewed in the ECDIS Pick Report. Where additional information is needed to explain the NM an associated picture file displays the ENC superimposed over the current paper chart information.


‘No Overlay’ feature

Where there is no ADMIRALTY paper chart at equivalent scale to the ENC, UKHO is not able to compare coverage and add additional information. In these areas, the AIO shows a grey hatched polygon labelled ‘No Overlay’.


ADMIRALTY paper T&P NMs may occasionally display within a ‘No Overlay’ polygon if the information has been published for smaller scale paper charts and is also relevant at a larger scale. Additional information, such as local T&P NMs, may be available in these areas from other sources. When navigating in these areas, seafarers should ensure that other sources of information such as local web sites, Navtex, port notices etc. have been consulted.

Passage Planning

SOLAS Chapter V states that all information relevant to the passage should be considered during planning. Appropriate scale, accurate and up-todate charts are to be used for the intended passage, as well as any relevant temporary Notices to Mariners.

Producer nation policy

Most countries now include temporary information in their ENCs and it is received on your vessel as a normal ENC update or new edition. This means that you can see the change on the ECDIS and use the pick report to obtain more information in the normal way. The ECDIS Route Assessment tools will automatically assess the temporary information because it appears as standard ENC objects. Your passage plan should be compiled as normal using what you see displayed on your ECDIS along with the pick reports. Some nations do not describe the information as ‘temporary’ or ‘preliminary’ in their ENCs; they simply issue updates as required.

ECDIS symbology

In August 2017, the S-52 Presentation Library 4.0 introduced a ‘d’ symbol for temporary information.

'd' symbol

It is displayed when the ENC producer codes a feature with time-based attributes such as start or end date and can be used for seasonal buoys, traffic separation schemes etc. You can also insert a date or date range into your ECDIS to display date dependant features.

Using AIO

You should have AIO active on your ECDIS screen during passage planning. Use the ENCs and route checking in the normal way, noting any features that are described in the pick report as being temporary. Check your route with the date set to the planned passage time. You may see coloured polygons that are associated with ADMIRALTY paper T&P NMs issued by the UKHO. The T&P NMs will be giving you additional information that is not already included in your ENCs. You should then open the text of the notice using the ECDIS Pick report to assess and include the information in your passage plan as necessary. You may wish to annotate your ECDIS display with key information from the T&P NM, so it is available as a prompt for watchkeepers if you prefer to hide the AIO during passage monitoring. If you use the mariner’s notes function on your ECDIS to mark the temporary items of interest, your notes should be checked against each week’s AIO update.


ADMIRALTY paper T&P NMs are not issued as corrections to electronic charts. Audit and compliance inspections require you to demonstrate that you are working with the latest ENC updates for your passage plan. You are also required to demonstrate that you have a system in place to reasonably obtain and assess temporary information.

Temporary information for digital navigation can be obtained from:

1. The information encoded in the ENC.

2. AIO distributes some extra information that may not be included in ENCs, where there is equivalent coverage by ADMIRALTY paper charts.

3. Other sources on board such as Navtex.

4. Local authorities, such as agents or port authorities.

Where the information is included in the ENC, you do not need to assess paper chart notices as part of their passage plan, unless you are navigating with paper charts.

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