Use of third party data and H-Notes

How to propose a new survey, what data the UKHO requires for a nautical chart, and how to report safety critical information or errors in our products

Hydrographic notes

Please notify us if you discover or suspect any of the following by submitting the appropriate Hydrographic note.

  • New dangers to navigation
  • Changes in aids to navigation
  • Errors in any navigational publication.

The Mariner’s Handbook (NP 100) Chapter 8 contains details of the information you’ll need to send. If practicable you should also contact the originating hydrographic office when navigating on IMO-approved non-UKHO nautical charts. Please also comply with national and international law when forwarding such reports.

If giving the information on paper please use either the version below or that included in NP100. NP100 will be updated with these later versions at the next edition.

H-note forms

Supporting information

Chart images and photographs - sent either with the hard copy or as attachments to the electronic copy - will help us to clarify your report.

Any format is acceptable. Those most commonly used are Word, Excel, JPEG, TIF, and AutoCAD. File sizes of the hydrographic notes range from approximately 61Kb to 70Kb; however the size of a returned email would depend on any additional attachments that have been made.

Email your completed form to or fax it to: +44 (0)1823 352561. For urgent information fax to +44 (0)1823 322352 or send by email.

Once we’ve received and processed your data, we’ll acknowledge receipt of it by post or email.

How to propose a hydrographic survey

Survey areas are prioritised using a risk analysis methodology but the Maritime and Coastguard Agency (MCA) also welcomes recommendations for areas needing assessment. Send your suggestions to

Typical indications of an area requiring a new survey

  • Old underlying survey data (check using the source data diagram on the latest chart)
  • A change in traffic patterns (eg, increases in cruise ship visits)
  • An accident occurring due to inaccurate or incomplete survey data
  • Changes to the seabed due to sand-wave movement / channel migration

Use of third party data on a nautical chart

If you are involved in producing hydrographic surveys, whatever their primary purpose, they may also be useful to our work. If possible, we would like to use them in the compilation of a new nautical chart. If so, we would really appreciate a copy of your survey to help improve the safety of mariners, but please read this first.

You don’t need to carry out your survey to full charting standards for it to be of use. Even without a full search for dangers, a modern survey can increase our knowledge of the seabed.

To help us get the best out of your survey please follow the advice below. Even if you’re unsure about these requirements, we’d still like to receive a copy of your survey. It may reveal changes that should be shown on the chart as a ‘less water reported’ legend. It may even prompt us to carry out a full survey.

Our Bathymetric Data Centre (BDC) is always happy to give help and advice on the requirements for gathering hydrographic data. Often minor changes to how your data is gathered and presented can make it much more useful for charting action.

The minimum information required

  • A copy of your final survey drawing and / or final digital dataset. The digital data may be in a simple ASCII ‘xyz’ (latitude, longitude, depth OR grid E, grid N, depth) format. The drawing can be in hard copy, but we would prefer a digital file if possible (.tif, .pdf or CAD)
  • If the data has been passed through a gridding or binning process to produce the final drawing or dataset, then a copy of the pre-gridding dataset would be beneficial. Gridding and some binning techniques may cause the shoal depths to be lost
  • A note of the horizontal datum to which the positions are referred (or the grid, if appropriate)
  • A note of the tidal datum to which the depths have been reduced
  • The soundings should preferably be reduced using observed tides (not predicted tides from tide tables)

This basic level of information will enable us to accurately position the data and adjust the depths as necessary to chart datum. We can render surveys to this standard from scientific, environmental, engineering and similar projects without adding significantly to the cost of the work.

A metadata form listing the required and preferred information can be downloaded and rendered with data to ensure that we have all the necessary information.

H275 - Metadata Report for Bathymetry Deliverables to UKHO

This file may not be suitable for users of assistive technology.

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Preferred information if available

Please try to achieve as much as possible of the following:

All data should be in digital form, ideally in one of these formats:

  • Caris HDCS directory (i.e. ‘HIPS’)
  • Simrad PROC directory
  • Generic Sensor Format
  • Fledermaus PFM
  • Simple ASCII ‘xyz’ is acceptable if the other formats are not available

If a hard copy plot and / or .dwg drawing is available please also supply this, as it helps us to check that the digital data is complete. Drawings may also include useful non-bathymetric detail, such as coastline and details of construction projects. Please record any differences between the digital data and the drawing, especially if depths on the drawing have been edited but the edits have not been applied to the digital data.

Cleaned digital data should have rejected soundings included, but flagged as deleted. The method used in any data-cleaning (eg, shoal- or median-biased) should be clearly stated

Digital data should be full density (ie prior to any gridding, binning or thinning being applied).

Ideally, the accuracy of both the depth and position of soundings should meet IHO S44 Order 1 requirements. Also, the density of the data should be such that the minimum target sizes stated in IHO S44 Order 1 are always detected. A report should describe how the data was gathered and processed.

It is particularly useful if the report can include:

  • A list of the equipment and software you used, and the personnel involved
  • How you set up and used the positioning equipment
  • How you set up and levelled the echo-sounder transducer (are depths to the waterline or to the transducer?)
  • How you measured tides, levelled the tide pole or tide gauge and reduced depths to chart datum. NB: A levelling diagram is a useful method of confirming that datum adjustments have been carried out correctly
  • Reports written in the Royal Navy ‘Electronic Report of Survey’ Microsoft Word template (available on request)
  • Data that fully complies with all aspects of IHO S44 Order 1

Remove spurious data from the dataset

Noise typically generates false shoal depths. The surveyor is in the best position to determine which apparently shoal features are real and which are not. Simple surveys carried out by hydrographic survey companies using single-beam echo-sounders are normally rendered to a standard of this type. It can be misleading to pass false shoal depths through to the final chart – in order to avoid such a feature, a vessel may have to follow a course that is more dangerous than necessary. A clean dataset will remove a lot of uncertainty when it is processed, but see below for retaining soundings. If you require further information about supplying swathe bathymetry surveys or if you need help making your data available for charting use, then please contact the UKHO Bathymetric Data Centre at

Published 29 August 2014
Last updated 16 July 2015 + show all updates
  1. Addition of different data types when using third party data on a nautical chart

  2. H102 V8 published

  3. First published.