What is a Map

What is a map: Unlike an aerial photograph, which shows everything that can be seen, a map does not. Basically a map is a plan of the ground on paper and is selective in what it shows.

The cartographers choose a selection of small objects to most likely be of help to the map user, like paths, streams and tracks, and plots their correct position on the map using symbols. These symbols, are called conventional signs.

Land maps are designed to show characteristics of the land surface in as much detail as space on the paper permits, consistent with legibility. Thus at very small scale it is possible to depict a very large area showing relatively sparse detail, while at large scale a much smaller area can be depicted in proportionally greater detail.

In general, maps and charts are designed to satisfy the majority of user needs.

The margin on each map contains a key, which lists and explains every class of object shown on the map, together with it's symbol, the margin also contains other technical information.

Heights in Metres

This information is located in the top left hand corner of a Ordnance Survey 1:50,000 scale Landranger series.

Explorer 1:25,000 scale

On the Explorer series of maps, 1:25,000 scale, this information can be found in the Map Legend under Heights and Natural Feature. It is advisable to check this as it can differ on different map sheets and in low lying areas. Another advantage of 1;25,000 scale explorer maps is that it shows the field boundaries, indicated by thin black lines criss crossing the map area. However the lines only state that a field boundary is or was present it does not indicate as to wether it is a hedge, wall or fence in some cases it could possibly be an earth bank.

Information Contained on a 1:50.000 Ordnance Survey Landranger map.

• Outer margin latitude and longitude. Inner margin grid coordinates, eastings along the top and bottom. Northings left and right hand sides.
• Top left corner, heights in metres (contour interval).
• Top centre of the map, magnetic, grid and true north pointers, also information required to calculate the grid magnetic angle.
• Right hand side, title of the map, sheet number, scale, customer information, communications information, general information, tourist information and technical information.
• Bottom centre of the map, measuring, measuring scale in kilometres, statute miles and nautical miles.

Representation of Detail (Types of detail)

Detail is usually considered under general headings as follows:

• Natural features including vegetation.
• Communications
• Buildings, villages and towns.
• Miscellaneous cultural detail.
• Boundaries.

Methods of Representing Detail

• Area Detail. Areas such as lakes, woods, built up areas are usually shown by colour tint.
• Line Detail Where detail has length rather than width, eg, roads, rivers and tracks conventional signs are used when the width of the feature cannot be shown adequately to scale.
• Point Detail When detail has significant positions but no significant size at a given map scale, eg, trig points and spot heights, conventional signs are used.
• Conventional Signs Different types of detail can also be shown by conventional signs used in combination. Thus a river may be shown as tidal or non tidal by the colours used to represent its banks. Woods may be shown as decidous, coniferous or mixed, by the symbols within an area of colour tint.
• Colour Different colours are used to represent different classes of detail and some conventional uses are given as follow:
• Blue - All water features.
• Green - Vegetation.
• Brown - Contours and sand.
• Black - All outlines, cultural details, but may be used in conjunction with other colours.
• Description Where no other method is available items of importance may be described in words or abbreviations, eg, ford, FB (foot bridge).
• Buildings, Villages and Towns When scale permits buildings are shown in outline with a filling. Small buildings may be shown by solid black conventonial signs.
• Coastal Features Coastlines are usually shown in black to represent the mean high water mark, however some map series show the high water mark in blue and the map user should always check the marginal information. The low water mark may also be shown, and and the nature of the foreshore may be indicated by symbols representing sand, mud or rocks. Coastal cliffs are shown by symbols, black usually, otherwise brown the same colour as the contours.
• Railways are shown in black by line symbols which may take various forms (1) Plain lines (2) Lines with single or double crosses (3) Diced lines.
• Vegetation At 1:50,000 scale a green tint is used frequently in conjunction with symbols to indicate which type of trees, ie, conifer or decidous.
• Water Features and Roads, Paths and Tracks (See seperate page)

Ordnance Survey 1:25,000 Explorer Series

Conventional Signs

Because map margins are frequently folded out of sight, or perhaps even cut off. It is essential that users become familiar with all the information they contain. it is important that the user to note that conventional signs can change, new signs can be introduced, whilst others could disappear.

Note: Flash cards of conventional signs, can be downloaded free from the Education section of the Ordnance Survey web site.

Taking Care of Your Map

Because maps are so expensive, it is in your own interest to take care of them. Some maps are now produced with a water proof coating but again these cost a bit more. the best way to protect your map is to keep it in a map case when in use, another way is a size A4 clear sealable freezer bag, cheap but ideal. If you need to mark your map use a pencil, and if your map does get wet let it dry naturally.

In Date Maps

Maps used should be fairly up to-date, information on old maps should be treated with caution.

Folding Your Map (see slide below)

Index to Adjoining Sheets

The locationof the map sheet relative to other map sheets in the series is shown in a diagram in the margin, thus enabling the user to identify immediately the surounding sheets.

Printing Note

The printing note will usually be found in the bottom right hand corner of the map and will consist of a string of numbers in the form 4000/5/86/4270R. This indicates that 4000 map sheets were printed in May 1986. Again this can provide a useful clue to the user. If the production note indicated that the map was produced in 1976 and the print note was dated 5/86 the probability is that the map would still be substantially up-to-date, ie, there had been so little change that it had not been worth producing a new edition.

The map series number identifies both the area and the scale of the map in accordance with a standardized world wide series designation system. The sheet number identifies the particular sheet within the series and the edition number indicates the number of times the map has been revised. the suffix to the edition number identifies the publisher of that particular edition, eg, GSGS = Geographical Section General Staff.