Marginal Information of Topographic Maps

A map could be compared to any piece of equipment, in that before it is placed into operation the user must read the instructions. The most logical place to begin when reading a map is the marginal information and conventional symbols, where useful information telling about the map is located and explained. All maps are not the same in terms of layout and information, so it becomes necessary every time a different map is used to examine the marginal information carefully.

Printed around the border or margin of the map are the information and additional facts about the specific map sheet that a given user is reading. This is referred to as Marginal Information. They are the basic components of a map since they give supportive details to make a map well defined and understood.


Marginal information found in topographic maps include the following;


1. Map Title (or Map Sheet Name)
Map title is the name or heading of the particular map sheet. It is usually printed in bold letters on the top of the map sheet. Usually, a map sheet is named after its most prominent cultural feature e.g. largest settlement and important town, or the largest natural physical feature on the map like a mountain, lake, forest or crater. Sometimes, map sheet titles can also indicate the information that the map user is expected to find on the map.

 2. Map Identification
Map identification refers the information about the identity of a particular map sheet. This information is useful to anyone intending to use or purchase a similar map. Thus, if one quotes this information, it will be easy for the survey department personnel to find the required map sheet. Map identification consists of three elements which are usually used when identifying any map sheet. These are the map series number, the map sheet number, and the edition designation.

·         Map Series Number

A map series refers to a group of maps having the same scale and cartographic specifications designed to cover a particular geographic area. It may also be a group of maps that serve a common purpose, such as the military city maps.

Map series number is a reference number that is used to identify a given map series. All map sheets in a given map series share the same map series number. It is usually expressed either as a four-digit numeral (1034) or as a letter, followed by a three- or four-digit numeral (Y321; T7110).

·         Map Sheet Number

Map sheet number is a reference number that distinguishes one map from other maps in the same map series.  Each map sheet has its own map sheet number. The map sheet number is usually shown in the upper right corner of the margin. It can also be seen in the center box of the adjoining sheets diagram, which is found in the lower right margin of the map.

·         Edition Designation       

Edition designation gives information about the publication of the map. It is a specific identification based on the publication sequence of a particular map. Edition designation is useful when identifying the up-to-dateness of the information shown on the map.

Edition designation consists of three parts; the edition number; the name of the agency responsible for producing of the map and the year the map was published. Example: Edition 4-AMS 1984.

The edition numbers run consecutively i.e. They increase at each revision. Thus, a map labeled with a higher edition number contains more recent information than the one with a lower edition number. The letters following the edition number indicate the abbreviation of the agency which produced the map. Some of the common agencies include; geographical section general staff (GSGS), united states geological survey (USGS) and directorate of overseas surveys (DOS). The year on the edition designation indicates the time the map was published and it is important when determining how accurately the map data might be expected to match what you will encounter on the ground.

All the information about map identification is usually enclosed in a box or placed together in a panel as shown below

3. Legend

A legend (also known as a key) is a table which explains the meanings of the conventional symbols, colors, and abbreviations used on a corresponding map. A legend consists of each symbol shown on the map, with a short description of its meaning. However, it should be noted that the legend simply includes information of all maps on a given map series. Thus, not all information contained in the legend will be found on the map.

This figure shows a legend from one of the Directorate of Overseas Survey's Topographic maps series Y742

4. Scale

To create an accurate picture of the landscape on paper, everything has to be made much, much smaller. This is done by scaling down the actual size of the land. The amount by which the actual size of the earth’s surface has been reduced down in order for the map to be drawn is known as the scale of a map. The scale of a map basically gives the ratio between the distance on a map and the corresponding distance on the earth’s surface.

On the map, scale is usually represented in two ways; as a ratio scale and as a linear scale.

For the example below, the ratio scale is 1:500,000. What this means is that one unit on the map represents 500,000 same units on the ground. On the map sheet, the ratio scale can be found in the upper left margin after the map sheet name, and in the lower margin of the map sheet.

And just below the ratio scale, is the linear scale or sometimes called the bar scale. A linear scale is usually in form of a horizontal bar and it can be used to make fast estimates of distance on the map.

5. Map Borders

A map border is a framework of the map understudy. It identifies exactly where the mapped area ends. Most of the topographic maps usually have two borders; the neatline and the borderline. The neatline only encloses the mapped area, while the borderline encloses both the neatline and mapped area.  The borderlines are usually thicker than the neatlines.

Maps may have only one border, but cartographers prefer to use both the borderline and the neatline to make a map more visually appealing. Usually, the distance between the borderline and the neatline is always the same on all sides of the map.

6.. Index to Adjoining Sheets /Adjoining Sheets Diagram

In the margins of most topographic maps, there is usually a box containing 9 squares whereby the central square (usually shaded) represents the map that is being used at the moment. The other squares represent the maps surrounding the map sheet being used. This box is what is referred to as the index to adjoining sheets diagram. The index to adjoining sheets diagram provides information of the neighboring map sheets by showing the sheet number and names of the neighboring sheets. The information in the index to adjoining sheets diagram is important to a map user in case he/she needs to purchase or refer to a particular map in the series.

 7. Declination Diagram

Early maps almost always had an arrow indicating to the direction of the geographic north pole-called the north arrow. By showing the north direction, it is easy for the map user to identify other important directions like west, east and south

However, in modern topographic maps, the information regarding the direction of north is given in the form of a diagram known as the declination diagram. This diagram is usually located in the lower margin of the map sheet

The declination diagram shows the angular relationship between the three types of north: true north, magnetic north, and grid north.  The information presented in this diagram relates directly to the orientation of true north, magnetic and grid north; and the magnetic declination of the mapped area, as calculated from the center of the map sheet in the survey year indicated.

The year in which the magnetic declination was measured and the annual rate of change of the declination is also stated in this diagram

Ø  True north or geographic north is the direction towards the North Pole from any place on the earth’s surface. On the declination diagram, the line of true north is shown with a star on top.

Ø  Magnetic north is the direction determined by a magnetic compass needle. The magnetic compass needle usually points towards the magnetic north pole. On the declination diagram, a magnetic north line is usually shown with half an arrowhead on top.

Ø  Grid north is the direction shown by the vertical grid lines on maps drawn using UTM grid system. Grid north is useful because it allows you to use UTM grid lines on your map as the north reference. Unlike true and magnetic north, the line of grid north is usually bare on the declination diagram

Ø  Magnetic declination is the angle that lies in between the true north line and the magnetic north line.

Recommended to read: The declination diagram on topographic maps

8. Name of Publisher and Copyright Owner of the Map

Topographic maps are accurately drawn and published by a given authority. The department for surveys of each country is usually in charge of producing maps after carrying out the required survey. It may also do this with the assistance of overseas organizations such as the ‘Directorate of Overseas Survey (D.O.S) of England. A large number of topographic maps have been produced by D.O.S in England on behalf of African governments. However, the permission for reproducing the map extracts can only be given by the copyright owner.  In most cases, the government of the country concerned is the copyright owner of the given map extract.

It is important for the name of the publisher whether (individual cartographer or an institution) and the copyright owner to appear on the map sheet. This may help the map users to make necessary consultation with the cartographer to have clarification on details about the area which has been mapped or request for the permission of reproducing the map from the copyright owner of the map.

9. Index To Boundaries Diagram

The index to boundaries diagram, which is a miniature of the map, shows the administrative boundaries that occur within the mapped area. It enables a map user to identify the administrative units such as in states, provinces, counties, cities, and towns; that appear on the main map.

This diagram is usually found in the lower margin of map sheets

10. Reliability Diagram

When a map has been compiled from several sources, a reliability diagram may be provided in the bottom margin of the map sheet to show the extent of coverage of the basic sources for different parts of the sheet.

The reliability diagram contains graphic references to the reliability of the sources used and indicates the methods by which the map was made, dates of photography, and r the degree of reliability of different parts of the sheet

This diagram will be found on maps only when the reliability of the information compiled is below the standard which is normally expected at that scale and in that area.

This figure shows a reliability diagram from one of the U.S Army Map Service AMS series Z501 (Durban 1:250,000 topographic maps). Notice that the diagram indicates which areas of the map were compiled from different sources, and may thereby have differing levels of reliability or uncertainty associated with them.

If you need to know the definition of any geographic term, word, or vocabulary found in this post, click here to be redirected to the Glossary of this blog.