Changes in Admiralty Chart Specification

Extract

Users of Admiralty charts will be familiar with the fact that the specifications which are followed in respect of content and design evolve continually; some of the changes are in response to suggestions put forward by users. It is intended, for example, to add the morse identification of racon signals on charts, following a suggestion by Trinity House. The Hydrographer is always anxious to encourage comments from sea and the Chart Users' Advisory Panel is dedicated to that end. Some changes result from new developments in the navigational field: the representation of vhf radio lighthouses, for example, is now being considered so that they may be charted by symbol when they emerge from their present on-test status to become fully operational. Other changes stem from office considerations, such as new cartographic techniques or the requirements of effective maintenance of the published charts. The more important of these changes are announced through Admiralty Notices to Mariners as corrections to the Symbols and Abbreviations booklet, 5011, a document indispensable to chart users since charts do not themselves carry a key to the symbols used; over 40000 copies of 5011 have gone into circulation in the past two years alone. Other innovations, less significant or self-evident, are not normally announced by Notices to Mariners in this way but implemented through office instructions to the cartographic staff of the Department. Recent examples have been the decisions to include notes giving the relationship of charted latitudes and longitudes to WGS-based positions, so that SatNav observations can be reliably plotted on charts; and, on a minor level, to add the label ‘o’ (zero) to the drying line at intervals in the same way that other depth contours on metric charts are labelled with their values, a step deemed to be useful in case copies of charts have to be printed without the superimposed colour tints.