UK Admiralty nautical chart series

A series of approximately 3250 navigational charts covering the
world. The series is maintained by Admiralty Notices to Mariners issued every
week. New editions or new charts are published as required. Two thirds of the
series are now available in metric units.

In areas where the United Kingdom is, or until recently has been, the
responsible hydrographic authority - i.e. Home Waters, some Commonwealth
countries, British colonies, and certain areas like the Gulf, Red Sea and
parts of the eastern Mediterranean - the Admiralty charts afford detailed
cover of all waters, ports and harbours. These make up about 30 per cent of
the total series. Modern charts in these areas usually have a source data
diagram showing the sources from which the chart was compiled. The quantity
and quality of the sources vary due to age and the part of the world the chart
depicts. The other 70 per cent are derived from information on foreign charts,
and the Admiralty versions are designed to provide charts for ocean passage
and landfall, and approach and entry to the major ports.

The series contains charts on many different scales, but can be divided very
broadly as follows:

Route planning 1:10 million
Ocean planning 1:3.5 million
Coast approach or landfall identification 1:1 million
Coasting 1:300,000 to 1:200,000
Intricate or congested coastal waters 1:150,000 to 1:75,000
Port approach 1:50,000 or larger
Terminal installation 1:12,500 or larger

Charts on scales smaller than 1:50,000, except in polar regions, are on
Mercator projection. Since 1978 all charts on 1:50,000 and larger have been
produced on Transverse Mercator projection. Prior to 1978 larger scale charts
were on a modified polyconic projection referred to as 'gnomonic', not to be
confused with the true Gnomonic projection.

Most of the detail shown on a chart consists of hydrographic information -
soundings (selected spot depths) in metres (on older charts in fathoms or
feet) reduced to a stated vertical datum; depth contours; dredged channels;
and the nature of the seabed and foreshore. Features which present hazards to
navigation, fishing and other marine operations are also shown. These include
underwater rocks and reefs; wrecks and obstructions; submarine cables and
pipelines and offshore installations. Shallow water areas are usually
highlighted with pale blue tint(s). Also shown are aids established to assist
the navigator - buoys, beacons, lights, fog signals and radio position finding
and reporting services; and information about traffic separation schemes,
anchorages, tides, tidal streams and magnetic variation. Outline coastal
topography is shown especially objects of use as fixing marks. As a base for
navigation the chart carries compass roses, scales, horizontal datum
information, graduation (and sometimes land map grids), conversion tables and
tables of tidal and tidal stream rates.

本系列包含约3250张航海图，覆盖全球范围。该系列由每周发布的海军部海事通告进行维护。根据需要，会出版新版或新图。目前，该系列中三分之二的部分已采用公制单位。在英国及其曾负责的海洋测绘权区域——即国内水域、部分英联邦国家、英国殖民地以及如波斯湾、红海和东地中海部分地区等——海军部航海图提供了对所有水域、港口和港区的详尽覆盖，约占系列总数的30%。这些区域的现代航海图通常包含源数据图，展示制图所依据的数据来源。由于年代和所描绘的全球区域不同，数据来源的数量和质量有所差异。其余的70%则源自外国航海图的信息，海军部版本旨在提供海洋航线、登陆点、主要港口的进港和入港图。本系列包含多种比例的航海图，但可大致分为以下几类：航线规划（比例1:1000万）、海洋规划（比例1:350万）、海岸接近或登陆点识别（比例1:100万）、沿岸航行（比例1:30万至1:20万）、复杂或拥挤的海岸水域（比例1:15万至1:7.5万）、港口进港（比例1:5万或更大）、码头设施（比例1:1.25万或更大）。比例小于1:5万的航海图，除极地地区外，均采用墨卡托投影。自1978年以来，所有比例1:5万及以上的航海图均采用横墨卡托投影制作。1978年之前，更大比例的航海图采用一种称为“正形投影”的改进多圆锥投影，需与真正的正形投影相区分。航海图上所展示的详细信息主要由海洋测绘信息组成——包括以米为单位的水深（在旧图上以英寻或英尺为单位）、深度等深线、疏浚航道以及海底和海岸的性质。对航行、捕鱼和其他海洋作业构成危险的特性也一并标注，包括水下岩石和珊瑚礁、沉船和障碍物、海底电缆和管道以及海上设施。浅水区域通常以浅蓝色色调突出显示。此外，还包括为协助导航者而设立的辅助设施——如浮标、灯塔、灯光、雾号以及无线电定位和报告服务；以及关于交通分隔方案、锚地、潮汐、潮流和磁差的信息。海岸地形轮廓特别展示了对用作定位标记的有用物体。作为导航的基础，航海图上还包含罗盘玫瑰、比例尺、水平基准信息、刻度（有时包括陆地地图网格）、转换表以及潮汐和潮流速率表。