Topic 3: Map Reading and Interpretation-Geography Form Two

MAP READING AND INTERPRETATION

Definitions of Map

– Map is a representation usually on a flat surface of the whole or a part of an area on a flat surface like cloth, wall, piece of paper etc. For example a city or country, which shows its main features, such as its roads, rivers, mountains etc

OR. Map is a symbolic depiction emphasizing relationships between elements of some space, such as objects, regions, or themes.

Map reading is the process of identifying features on a map by using symbols and signs or names. This technical work requires certain skills that any map reader must possess.

Map interpretation is the interpretation of the symbols and signs used on map into ordinary language by indicating the features they represent and draw logical conclusions from the information as represented by the symbols.

Cartography is the study of making or drawing maps

Cartographer is a person who draws or produces maps

TYPES OF MAPS

Maps can be categorized based on various criteria. One common way to classfy them is by their purpose. Based on this criterion maps are generally divided into two main types: GENERAL PURPOSE MAPS and THEMATIC MAPS.

A: GENERAL PURPOSE MAPS

General purpose maps are maps designed to show a wide range of information about an area.

They are used for many different purposes, not just one specific use. They show both physical and human features such as relief, rivers, roads, towns, boundaries, and settlements.

Examples of General-Purpose Maps

1. Topographical Maps

• Show detailed physical and human features of an area.
• Include relief (using contours), rivers, forests, roads, settlements, and land use.
• Used for surveying, planning, geography studies, and navigation.

2. Political Maps

• Show administrative boundaries such as countries, regions, districts, and cities.
• Indicate capital cities, major towns, and borders.
• Used for government administration, education, and political studies.

3. Road and Railway Maps

• Show transport networks like roads, highways, railways, and stations.
• Help people to plan travel and transportation routes.
• Used by drivers, travelers, transport planners, and logistics services.

B: THEMATIC MAPS

Meaning of Thematic Maps

Thematic maps are maps that display specific and focused information about one particular subject (theme) in a given area. Unlike general purpose maps, thematic maps are designed to highlight one type of information only, depending on the purpose of the map. The information shown may include soil types, vegetation zones, crop distribution, population density, weather patterns, or urban planning features.

Examples of Thematic Maps

1. Population Maps

• Show the distribution, density, or growth of population in an area.
• Use shading, colors, dots, or symbols to represent population data.
• Help in planning social services, such as schools, hospitals, and housing.

2. Weather Maps

• Show weather conditions such as rainfall, temperature, wind direction, air pressure, and storms.
• Use symbols, lines (isobars), and colors to represent weather elements.
• Used for weather forecasting, disaster management, and climate studies.

3. Urban Planning Maps

• Show land use in towns and cities, such as residential areas, industrial zones, commercial areas, roads, and public facilities.
• Help planners to design, manage, and develop urban areas efficiently.
• Used by municipal authorities and urban planners.

ESSENTIAL ELEMENTS OF A MAP

The basic skills required in understanding how to read a map include Title, Scale, Key, Indication of the north direction, Margin/Boundary and Date of compilation.

1. Tittle

Gives the name of the country and the area where mapped. It helps the map reader to know what the map is all about. The heading is usually printed in bold capital used on the map

2. Scale 

Scale is a ratio between the distance on the map and actual distance on the ground. It is used to find actual distance and areas on the ground. On topographical maps scales are given in form of ratio or lines.

Types of scale

i. Large scale. Are those maps drawn to large scale size e.g. 1:10000 These maps gives a larger representation of small area, they are also more detailed (shows a lot of information). They represent areas like cities, towns and villages.

ii. Medium Scale. Are those maps drawn to medium scale size e.g. 1:100000 They show a moderate amount of details. They represent areas like districts, regions and countries.

iii. Small scale Are those maps drawn to small scale size e.g. 1:1000000 They give a small presentation of a large area; they show little content (little information) They represent areas like continents and the world.

WAYS OF EXPRESSING SCALE

I. Statement Scale (Verbal Scale or sentences scale)

• Expressed in words.
• States how much distance on the map represents on the ground.

Example:

One centimetre on the map reperesent five kilometres on the actual ground.

II. Representative Fraction (RF) or Ratio Scale

• Expressed as a ratio without units.
• Shows the relationship between map distance and ground distance using the same units.

Example:

1 : 50,000

This means 1 unit on the map represents 50,000 of the same units on the ground (e.g., 1 cm on the map = 50,000 cm on the ground).

III. Linear Scale (Graphic Scale)

• Shown as a straight line divided into equal parts.
• Each division represents a fixed ground distance.

Example:

A line divided into parts showing 0 1 2 3 4 km

Used to measure distances directly on the map using a ruler.

3. Key / legend

Key is a feature which explains the signs and symbols which are used on the map. Not all symbols which are used in the key are applicable to the particular map but all signs and symbols applied on the map are shown on the key. Definition of terms which should be added on others terms under the tittle “Basic skills of map reading/Essential elements of a map” are ” margins/Bounder

4. North direction.

It gives an idea about the orientation of the map especially in identifying where the north direction is.

5.Margin/Boundary.

A frame which borders the map. This guide and limit the map user in reading and interpreting the map. The aim of the margin is to enclose the area covered by the map

6. Date of compilation.

Gives the publisher name and when the map was published. This date is important because physical and human settlements features changes with time but the map drawn representing the land does not. For instance between 1960 and 2007 Dar es salaam has changed in many ways.

7. Source

The source shows where the map information was obtained from. It may include survey departments, satellite images, aerial photographs, or official publications. The source helps users to judge the accuracy and reliability of the map. Example: Source: Surveys and Mapping Division, Tanzania

8. Grid

A grid is a network of intersecting lines (eastings and northings) drawn on a map. It is used to locate places accurately using grid references. Grids help in navigation, map reading, and identifying exact positions. Example: A point located at grid reference 436 782.

9. Authorship

Authorship indicates the person, organization, or authority that prepared or produced the map. It shows who is responsible for the map content. This helps users to trust the map and give proper credit.

Characteristics of a Good Map

A good map is one that clearly and accurately communicates geographical information to the user. The main characteristics include the following:

1. Effectively communicates geographical information

A good map clearly shows the intended information so that users can easily understand the geographical features being presented.

2. Clear and easy to read o The map should not be overcrowded.

Symbols, names, and lines must be well spaced and readable.

3. Contains all essential elements of a map

These include title, scale, key (legend), direction (north), source, grid, and authorship. These elements help users correctly interpret the map.

4. Accurately represents actual places and distances

Distances, directions, and locations shown on the map should closely match real ground conditions.

5. Displays relevant information only

A good map includes information that is related to its purpose and avoids unnecessary details that may confuse users.

6. Uses symbols, colours, and styles consistently

The same symbols and colours should represent the same features throughout the map. This helps avoid misunderstanding and improves clarity.

7. Contains up-to-date information

The map should reflect current conditions, such as new roads, boundaries, or settlements.

Importance of Maps

They provide basis for description of geographical phenomenon

They are useful for traveling purpose i.e. they guide people to reach their destination

Maps are useful for storage of geographical information

4.They are important for field studies

They are important for land use planning

They are useful for military purposes e.g. during wars.

READING AND INTERPRETING MAPS

Topographical maps are types of maps which describe the physical (natural) and manmade (artificial or cultural) features of a given area. The physical features include relief, vegetation, and drainage, among others. Some of the cultural or artificial features are roads, railways, cities, towns, dams, schools, and many other structures built by man.

1. DRAINAGE

Drainage is the plan or layout of the river with its tributaries until it reaches its destination i.e. lake, main river, swamps or an ocean, therefore the concept drainage includes rivers , swamps, lakes, waterfalls, flood areas

Note: The common drainage shown on the map is rivers, swamps, lakes and ocean.

But expect to see even waterfalls especially on coloured topographical map.

DRAINAGE PATTERNS

This is the plan or layout of the river with its tributaries, or the network displayed by a river and its tributaries. Drainage of the river usually posses different network/system depending on the way how tributaries convey to the main river and the general appearance, hence drainage pattern

Types of Drainage Patterns

The following Patterns are Commonly Displayed in Topographical Maps:

1. Dendritic Pattern

Is a pattern in which its tributaries convey (join) to the main river at an acute angle resembling to the shape of tree trunk and its branches. Dendritic pattern are common in areas of gentle slope and of uniform (homogeneous) rock hardness. Therefore it can be made from granitic or metamorphic rock

2. Trellised Pattern

Is the pattern in which its tributaries convey or join to the main river at almost right angle. This type is commonly found in areas with severe cracks or fractures mostly to the rocks with an alternate hard and soft rock. Therefore this is associated with sedimentary rocks.

Trellised Pattern

3. Radial Pattern

Is the pattern or layout in which its tributaries flow outward from the center (summit) or at the peaks of mountains. Its pattern resemble a spoken ring of bicycles where stream flow out in every direction from the center. Therefore radial drainage pattern is commonly associated with volcanic mountains /region composed of granitic rock or igneous rock

4. Centripetal Pattern

Is the pattern in which almost all streams are following from all direction converging to the center can be to the swamp, lake or depression. The determinant factor of stream flow is a slope.Therefore the drainage pattern can be associated with sedimentary rock.

5. Rectangular Pattern

Is a pattern which resemble trellised, but it has tributaries joining the main river at a right angle. The pattern is common in areas which are faulted. Therefore can be found along sedimentary rocks/granitic rock or any faulted rock.

Rectangular Pattern

6. Parallel Drainage Pattern

This consists of a series of streams running parallel to one another. In some cases, streams may flow into one big river. It is common in areas of uniformly dipping rocks such as fault scarps or recently emerged coasts. Rivers Athi, Nairobi, Ruiru, Chania, Thika and Sagana in Kenya.

 

Parallel Drainage Pattern

2. ROCK TYPE / STRUCTURE

The surface rock on the topographical maps is not directly indicated. They some clues are needed in order to identify rock type and structure of the mapped area. The Indicators Used to Show the Type of Rock presented in a certain Area:

1. LAND FORMS

Land forms shown on the topographical maps help on interpretation of rock type for example:

1. The presence of volcanic land form such; crater, caldera, name of the volcanic mountains suggest the presence of igneous rock.
2. The presence of erosion and depositional features such as depression, sand dunes, coral reef suggest the presence of sedimentary rock. Flood plain suggests sedimentary rock.
3. The presence of highland with steep slope indicated that rock are hard and resistance rock that may indicate presence of metamorphic rock.

2. VEGETATION

1. Thick forest suggests the presence of igneous rock.
2. Poor vegetation cover suggests the presence of sedimentary rocks or metamorphic rock.
3. Nature of the rock. Absence of streams indicates that the rocks are permeable. Thus this depict that the rock is soft which can either be sedimentary, limestone or sandstone.
4. Presence of many streams on surface, indicate that the rock are impermeable such as igneous or granitic rock.

3. RELIEF

Read the contour and the conventional symbols or signs on the map to identify types of relief. Can either be highland relief with lower arts or lowland relief. Describe the relief with associated land forms. When you determine types of relief first look on the units on vertical interval (V.I) whether the unit is in meters or feet. If units are in feet take the highest value the convent into meter finally determine type of relief (1m=3.3ft)

 

Relief

4. CLIMATE

Climate is the average weather condition experience in a given area over a long period of time not less than 30 years. Topographical maps may be used to identify the climate of given mapped area. Some hints used in interpreting climate from topographic map Latitude of the area.

1. Distance from equator used to determine kind of climate of a certain area. For example the area with latitude 5 degrees north or south of equator the area is considered to be in equatorial climatic condition while the area between 5 to 15 N/S is in tropical climatic condition, 15-30 N/S of the equator imply Semidesert 30-40 N/S implies desert climate or Mediterranean climate.
2. Water bodies. a general high density of streams indicates that the area receives high rainfall, presence of low density or seasonal streams, salt lakes and boreholes indicate aridity.
3. Vegetation, presence of forest in the map indicates heavy rainfall while woodland vegetation indicates moderate rainfall. shrubs, thickets and grassland indicate dry condition or light rainfall Crops, crops grow in those areas where water and temperature conditions are favorable for their growth. For example area with tea, coffee and sugar cane indicate that area receives heavy rainfall.
4. Crops such as cotton, sisal and sorghum indicate medium rainfall Relief/altitude, altitude of features such as high mountain or mountain ranges and plateaus tend to have orographic rainfall and forest making them makes their own mountainous climate. Mountains do also create their own climate due to effect of aspect which creates rain shadow.

5. HUMAN ACTIVITIES

A map may contain information on economic activities undertaking usually the following are shown on the different maps.

1. Agriculture: look on the presence of Rural settlement in absence of other activities scattered cultivation storage houses/center plantation or estate (indicate large scale agriculture) industry such as Ginneres, Hulleries and Decotecator. seldom symbols or signs are used e.g. S-sisal, CC-coffee, Su-sugarcane
2. Pastoralism: look on the presence of cattle market-cattle dips veterinary installation (Vet. Office)/center Creamers (lace where milk, cream butter and cheese are processed Scattered vegetation or dominated by scrub/shrubs) Bore holes (Bore holes (BH) or water hole (wh)
3. Mining: look on the presence of; symbols of PIC () and shovel (salt work quarrying Roasting Sign Tin-TN, Iron-Fe.
4. Fishing: look on the presence of; water bodies such as lakes, seasonal swamps, rivers, dams, ocean. These should be surrounded by settlement.
5. Trade and Transportation; look on the presence of Road, railway, towns and market (MKT)
6. Lumbering; look on the presence of; forest with track-roads ending on their edges. Saw-mill Sao hill forest -Note: thicket, scrubs/shrubs and bamboo trees cannot be exploited as a timber.
7. Tourism: look on the presence of; National parks, Game reserve Recreational centre’s e.g. museum, archives beaches etc Landscape e.g. crater depression etc.
8. Administration: Various administrative activities can be identified from abbreviations on the map. These are given in a list in the margin of the map. They include:
9. Provision of security as evidenced by the presence of a Police Station or Police

Post

1. Judicial services as evidenced by the presence of courthouse
2. Other administrative offices such as District Commissioner (DC)
3. Regional Commissioner (RC).

SETTLEMENT

A settlement is a place where people live. It may be as small as single house in a remote area or as large as a mega city.

Types of Settlement

There are two types of settlements which include, urban settlement and rural settlement.

• Urban Settlement; Is commonly found in areas of District administrative centers, Regional administrative centers, and Capital city of a country.
• Rural Settlement; Is an area where the majority of people approximately to cover 80% engage in agriculture

SETTLEMENT PATTERNS

It is a layout of dwellings in a particular place. The signs showing settlements on topographical maps are observed to have varied arrangement. The most common pattern include the following:

1. Dispersed Settlement Pattern

It is alternatively called scattered settlement pattern. The houses are widely spaced one to another

2. Nucleated Settlement Pattern

Houses and other related form are compacted to another.

3. Linear Settlement Pattern

Houses are concentrated along an elongated objected of economic significance like a road, river, railway lines and others

Factors Encouraging Settlements

A reliable source of water supply e.g. presence of permanent rivers, lakes.

Gentle slope i.e. people prefer to establish settlement in less hazardous areas

Good soil for agriculture

Pleasant climate condition

Transport and communication.

Ways of Showing Position on a Map

A place can be located by its name where it is found. A more accurate way of locating a place is the use of latitudes and longitudes, this method is used by scalars at sea and aircraft in their flights. Generally position of any place can be located by using;

• Place names
• Bearing
• Latitudes and longitudes
• Grid reference

Methods/ Way/ techniques of representing Relief features on Map

1. Contour Lines

These are lines drawn on topographical maps to join all places or areas with the equal height or attitude from the mean sea level. Contour are very important in determining relief features whether the relief is steep sided or gentle sloping. This measurement of heights shown by contour lines starts from the mean sea level which is regarded as zero height.

Contour Lines

2. Trigonometric Station

This is a point on a map with its exact height fixed usually on a hill top, mountain peak or other visible positions. They are the highest points on any locality. The trigonometrical points are commonly marked by a triangle followed by the numbers indicating the height for example Δ725

3. Spot Height

Spot height is a point on a map with its exact height above a known level e.g. from the sea level. The position and height of the points have been determined by surveyors. The spot height is marked with a dot followed by the numbers indicating height of the land for example .750

4. Layer coloring / Tinting

Is also done to show the relief features on the map, different coloring shades on the map to indicate different heights

5. Hachures

Huchures are short, broken lines drawn on a relief map showing direction and steepness of a slope

6. Form Lines

Form lines are usually unnumbered lines drawn on a map joining of nearly the same height areas, Are broken lines drawn between two contour lines

Form Lines

7. A Bench Mark (BM)

is a fixed reference point on the ground whose height above mean sea level is accurately known.

It is used in maps and surveying to show elevation (height) and help in representing relief.

How a Bench Mark is Shown on a Map

On topographical maps, a bench mark is commonly represented by:

• A small triangle (△)
• A dot (•)
• The letters BM written next to the symbol
• A number showing the height above sea level, usually in metres

Relief Features on Topographical Maps

1. SPURS

is a long, narrow ridge of high land that projects out from a hill or mountain into lower ground, usually between two valleys.

 

2. A ridge 

is a long, narrow area of high land that forms the highest line (crest) between two valleys or lowlands.

3. Escarpment

An escarpment is an area of highland with very steep slopes on one side and a gentle slope on another side. The steep slope of an escarpment is called the scarp slope and the gentle slope is known as dip slope.

4. Plateau

A plateau is an extensive highland region and whose top surface is almost flat. A plateau is easily identified on the map by the absence of contour lines on the higher land surface and with a series of contours close together on either sides.

5. Slopes

A slope the inclination or slant of the land. This inclination varies considerably, resulting in the following types of slopes A concave slope are widely spaced at the lower ground and closely spaced at the higher ground.

6. Col.

A Col is the land between two peaks of a mountain or in the mountain ranges.

7. Saddle (pass). A saddle is generally wider than a col. Saddles provide convenient passages across mountain ranges. Contours showing peaks are usually closed.

8. Valley. Valley is the low lying part of the land which is bound over higher ground and steep slope. Valleys are indicated by contours forming ‘V’ shape pointing the higher ground and some valleys have rivers flowing in them.

CROSS SECTION

Is a diagram or profile that shows a vertical cut through a landscape or feature. This used to show variation of relief across a region.

The following stages are followed in drawing cross section:

1. Two end points of the area in question are marked AB
2. Join the two points with straight line by a pencil
3. Take a piece of paper measure from point A to B
4. A vertical scale is now required after marking the values of contours on the paper.The horizontal scale of the cross section is in the same scale as that of the map from which the line AB is taken. The highest contour line on the map is 100m
5. The horizontal base line represents sea-level; the marked paper is placed along the base line so that A on the paper falls on A on the scale. Then each contour along the horizontal line is marked with a pencil and ruler, vertical lines are lightly drawn up to the line which represents the contour height.

INTER VISIBILITY

In reading the map it is important to know from a map whether one place is visible from another or not. In cross section two places A and B were to represent two observation points weather the two places are inter visible or not.

To explain inter visibility we look in the cross section if between the points (A to B) a mountain or hill develops we say the two points are not inter visible because the hill is an obstacle When the basin of depression develops we say the inter visibility, as a line of sight when drawn straight i.e. not obstructed But inter visibility can be affected by other factors such as buildings, vegetation etc.

 

GRADIENT

Gradient is the term refers to the measure of slope. Gradient/ slope are measured by comparing vertical distance to the horizontal distance. In map reading the calculation of gradient is done by comparing the vertical interval between two places and the horizontal distance between them.

Vertical Interval (V.I) is the difference in height between the two places; it can be obtained by subtracting the altitude of the lower point from the altitude of the higher point. V.I = highest contour

Lowest Contour The horizontal distance is measured on the map then it is converted into ground distance by the use of the map scale In calculating gradient both vertical and horizontal lengths must be brought to the same unit of length The formula for gradient Gradient =(Vertical interval ) / ( Horizontal distance)

Calculating Gradient

Example: Given; highest contour 700, lowest contour 300

V.I = 400m Length from point A to B is 8.4 cm Scale of map 1cm to 2km Calculate the gradient

Solution

Step 1: Change 8.4cm into ground /map scale 1cm to 2km 8.4cm to x =16.8km

Step 2: Change the ground scale into meters 1km =1000m 16.8km =? =16800m

Step 3: Gradient=(Vertical interval (V.I))/(Horizontal distance (H.D)) = 400m/16800m Gradient= 1/42

VERTICAL EXAGGERATION (VE)

Vertical Exaggeration (VE) is a technique used in maps, especially cross-section or profile drawings, to amplify (stretch) the vertical scale so that relief features like hills and valleys are more visible.

• It is done because the actual vertical height is often too small compared to the horizontal distance to be clearly represented on the map.
• VE makes the height differences more noticeable for easy interpretation.

Procedure to Calculate Vertical Exaggeration (VE)

1. Identify the horizontal scale (H) of the map o Usually given in ratio form, e.g., 1:50,000.
2. Identify the vertical scale (V) used in the profile o Usually drawn in cm per metre, e.g., 1 cm = 50 m.
3. Use the formula:

Vertical Scale

VE =

Horizontal Scale Both scales must be in the same units.

Example

If the map scale is 1:100000 and the vertical scale is one cm to 100m. Then the exaggeration is calculated as follows:

𝟏 𝟏

VE = ÷

𝟏𝟎𝟎𝟎𝟎 𝟏𝟎𝟎𝟎𝟎𝟎

𝟏 𝟏𝟎𝟎𝟎𝟎𝟎 𝟏𝟎𝟎𝟎𝟎𝟎

× VE= =10

𝟏𝟎𝟎𝟎𝟎 𝟏 𝟏𝟎𝟎𝟎𝟎

The vertical exaggeration is 10 times. This means the vertical scale is 10 times larger than the horizontal scale

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