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Types Of Maps – Navigation Charts


Contents

Introduction

Navigation Charts combine aspects of topographic, general reference and thematic maps and are produced as navigation aids for ships, boats and aircraft.  Specialist knowledge is usually required to read charts. 

Like topographic maps, charts are typically produced by government mapping agencies:

  • marine navigation charts are usually produced by a country's Navy and possibly also civil defence bodies and/or port management authorities
  • air navigation charts are usually produced by a country's Airforce plus a civilian agency which is responsible for civilian air traffic control and regulation

Also, navigation charts typically have well defined standards which are strictly adhered to.


Explaining Some Jargon – The Difference Between Maps and Charts

When people started making maps 5,000 years ago a distinction gradually emerged regarding maps of land and maps of the sea/ocean.

For the land they were called maps and for the sea/ocean they were called charts.  Both would map the coastline and its features.  However the chart was more likely to show great detail about the water and the water's edge, with little information about the land – the exact opposite of a map.  In particular, features which could be dangerous to ships (eg submerged rocks) were shown in as great a detail as knowledge and the scale (size) of the chart would allow.  Also, land features which would be an aid to navigation (eg cliffs/headlands or lighthouses) would be shown, while features which are important to maps (eg main roads or inland towns) would not be shown.

Another difference was that charts had specialist information which aided navigation, especially navigation out-of-sight of land.  This information included such things as water depth, location of lighthouses, significant coastal features (eg a mountain or a headland), compass roses and text notes (examples of text notes are 'area usually covered in fog', 'strong tides occur in spring' etc).

In the twentieth century, with the arrival of flight, a convention developed that maps which were specifically made to aid aeroplane navigation would also be called charts.  A key factor in this was that they also needed specialist information to aid navigation.


Marine Navigation Charts

The chart images used here are with the permission of the Australian Hydrographic Service; for more information regarding Australian marine navigation charts please visit their website www.hydro.gov.au.

Marine navigation charts (also referred to as nautical charts) are produced at a vast variety of scales – depending on the information available and the nature of the area being mapped.


Copyright Commonwealth of Australia.   Not to be used for Navigtion.   Extracts from 1:300,000 scale Australian Hydrographic  Chart AUS317 Indian Ocean Pulau Sawu to Ashmore Reef Copyright Commonwealth of Australia.   Not to be used for Navigtion.   Extracts from 1:300,000 scale Australian Hydrographic Chart AUS317 Indian Ocean Pulau Sawu to Ashmore Reef

These are extracts from an Australian charts which covers part of the Indian Ocean and includes Ashmore Reef.

The first extract is an example of the level of information that charts show over great expanses of ocean.  This includes information about the seabed depth below the surface of the water.  The numbers indicate known depth for an individual spot and the dotted line is an indication of lines of equal depth - generally called bathymetric contours (or isobars) to distinguish them from land contours.  The purple circle is a compass rose.

The second extract is the same as that shown in the first extract – it is shown here in a larger format for ease of reading.  See the section about maps being reproduced at different scales in the Marginalia Section.  Note that the level of information supplied about depth is far greater than on the first image; this is because small changes in depth in shallow water can be a hazard to shipping, whereas in deeper water it is not as critical. 




Copyright Commonwealth of Australia.   Not to be used for Navigtion.   Extracts from 1:37,000 scale Australian Hydrographic Chart AUS44 Timor Sea, Ashmore Reef

This extract from a chart of the Timor Sea has a great deal more information about the water depths around Ashmore Reef than the two extracts above from an Indian Ocean chart.  Note that the Indian Ocean extracts show only a few of the small reefs (the areas in green) within the lagoon, and most of these are shown as symbols (stars).  In this more detailed chart all the reefs are shown (and not symbolised) and greater detail is supplied regarding water depth.

These chart extracts offer good examples of how the scale of a map and its purpose dictate what can/is included.

Both are designed to enhance ships' safety, but in very different circumstances.  The first two extracts from an Indian Ocean map is designed for navigation over large areas, in deep water and this extract is designed for navigation in shallow waters around Ashmore Reef. 


Copyright Commonwealth of Australia.   Not to be used for Navigtion.   Extracts from 1:5,500 scale Australian Hydrographic Chart AUS154, Port Melbourne, Williamstown and Yarra River

First of all, note a characteristic of marine navigation charts – they supply a great deal of information about the water areas, but very little information for the land.  This is a busy port area and it is important that complex, accurate information is supplied to ensure that vessels don't 'run into' each other.  Note the additional information which is supplied compared to the Ashmore Reef.  These include:

  • a much more detailed coastline – including structures such as piers and jetties
  • marine navigation aids such as the location of marine lights
  • navigation control zones – eg shipping lanes and restricted areas.


The days of 'black-and white' charts (old 'fathom' charts) are over.  The International Hydrographic Organisation (IHO) international specifications recommend that nautical charts have a minimum of four colours (blue, black, grey and magenta).


Air Navigation Charts

Like the marine navigation charts, air navigation charts are produced at a vast variety of scales – depending on the information available and the nature of the area being mapped.  However, a fundamental difference between the two is the functionality – to state the obvious:

  • air navigation charts are used by fast flying aircraft which can be very high above the land and have significant safety concerns when landing
  • marine navigation charts are designed to be used by ships/boats on the surface of the water and they have significant safety concerns when in shallow water and when docking

Because of this, air navigation charts look very different to marine navigation charts.  However, like marine navigation charts international convention is that if the chart is coloured then special navigation information is shown in purple.  Unlike marine navigation charts, air navigation chart heights are always given in feet above sea level.

Copyright Commonwealth of Australia.  Airservices Australia, extracts from World Aeronautical Chart (WAC), Albany Copyright Commonwealth of Australia.  Airservices Australia, extracts from World Aeronautical Chart (WAC), Albany

These two examples of air navigation charts are from a World Aeronautical Chart 1:1 million scale charts and are designed for use by aircraft flying long distances.

With this in mind, the main landscape features which are shown on the map are those which could be easily seen from a high flying aircraft.  Cities and towns are also shown; as are places which have landing grounds (the round purple symbols).

An indication of the ruggedness of the land is given by hill shading and height values for individual high points in an area (the large black numbers).  Also, man-made features which could be a hazard to low flying aircraft are also shown – examples on these charts are the purple wiggly lines (power lines) and the purple triangles (towers and chimneys). 



Copyright Commonwealth of Australia.  Airservices Australia, extract from Visual Terminal Chart, Perth

Visual Terminal Charts are made for the purpose of aircraft takeoff and landing.  Note how this extract over Perth when compared to the extract above has a great deal more information including controlled airspace, the shape of landing strips and many more landscape features. 



Further Reading
Australian Hydrographic Service – Charts
http://www.hydro.gov.au/prodserv/prodserv.htm

International Hydrographic Organisation – Regulations of the IHO for International Charts and Chart Specifications
http://www.iho.int/iho_pubs/IHO_Download.htm#Standards

National Geospatial Intelligence Agency – Links to charts and other map products
https://www.nga.mil/ProductsServices/Pages/PublicProducts.aspx

Office of Coast Survey, National Ocean Service, National Oceanic and Atmospheric Administration (NOAA) – Learning About Charting and Surveying
http://www.nauticalcharts.noaa.gov/staff/education_learnabout.htm


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Last Updated: 23 Jun 2016