Topographical Maps - Solutions

 CBSE Class 11 Geography

NCERT Solutions
Chapter 28
Topographical Maps

1. Answer the following questions in about 30 words.
(i) What are topographical maps?

Ans.Topographic maps are detailed, accurate graphic representations of features that appear on the Earth's surface. These are also known as general purpose maps. These are drawn at relatively large scales. These maps show important natural and cultural features such as relief, vegetation, water bodies, cultivated land, settlements, and transportation networks, etc. In other words, it is a map of a small area drawn on a large scale depicting detailed surface features both natural and man made. Relief in this map is shown by contours.

(ii) Name the organisation which prepares the topographical maps of India.

Ans. Topographical maps under India and Adjacent Countries Series were prepared by the Survey of lndia till the coming into existence of Delhi Survey Conference in 1937. Since then the preparation of maps for the adjoining countries was abandoned and the Survey of India confined itself to prepare and publish the topographical maps for India as per the specifications laid down for the International Map Series of the World. Survey of India, is the National Survey and Mapping Organisation of the country, under the department of Science and Technology. It is the oldest Scientific Department of the Government of India.

(iii) Which are the commonly used scales for mapping our country used by the Survey of India?

Ans. Map scale refers to the relationship (or ratio) between distance on a map and the corresponding distance on the ground. For example, on a 1:100000 scale map, 1cm on the map equals 1km on the ground. The topographical maps of India are prepared on 1 : 10,00,000, 1 : 250,000, 1 : 1,25,000, 1 : 50,000 and 1: 25,000 scale providing a latitudinal and longitudinal coverage of 4° x 4°, 1° x 1°, 30' x 30', 15' x 15' and 5' x 7' 30", respectively.

(iv) What are contours?

Ans. Contour lines are the greatest distinguishing feature on a topographical map. Contours are imaginary lines joining places having the same elevation above mean sea level. In other words, these are imaginary lines joining all the points of equal elevation or altitude above mean sea level. They are also called "level lines". A map showing the landform of an area by contours is called a contour map. The method of showing relief features through contour is very useful and versatile. The contour lines on a map provide a useful insight into the topography of an area.

(v) What does the spacing of contours indicate?

Ans. On a topographic map, the contour lines follow a certain elevation across the terrain. Spacing in the contours represent slope. (a) If the lines are far apart, that means that there is little or no slope in that area of the map. When the lines are far apart it means that there's a long horizontal distance between places with different elevations.(b) By contrast, if the lines are close together, that means there is only a short distance between places with different elevations. That means it's a steep slope. (c) If the lines are practically touching, that means it's a very steep slope -- maybe even vertical.

(vi) What are conventional signs?

Ans. There are some internally determined standard symbols, signs and colours which are used to depict settlements, buildings, roads and railways are important cultural features shown on topographical sheets. When these features are exhibited through conventional signs, symbols and colours, it becomes easy to understand and interpret the map , Conventional signs and symbols are internationally accepted so that anyone can read any map anywhere in the world without knowing the language of that particular country. Conventional signs are designed to enable the maximum amount of information to be put on a map in the clearest way possible.

2. Write short notes on
(i) Contours

Ans. Some basic features of contour lines are: (a) A contour line is drawn to show places of equal heights.
(b) Contour lines and their shapes represent the height and slope or gradient of the landform.'
(c) Closely spaced contours represent steep slopes while widely spaced contours represent gentle slope.
(d) When two or more contour lines merge with each other, they represent features of vertical slopes such as cliffs or waterfalls.
(e) Two contours of different elevation usually do not cross each other.

(ii) 'Marginal Information' in Topographical sheets

Ans. Before a map is used, the user must read the instructions.The most logical place to begin is the marginal information and symbols, where useful information telling about the map is located and explained. All maps are not the same, so it becomes necessary every time a different map is used to examine the marginal information carefully.

Marginal Information: It includes the 1 topographical sheet number, its location, grid references, its extent in degrees and minutes, scale, the districts covered, etc. In other words, it provides information related to what exactly a topographical sheet is showing. Without this marginal information, it is not possible to derive any meaning from a topographical sheet.

(iii) The Survey of India

Ans. Survey of India, The National Survey and Mapping Organisation of the country under the Department of Science & Technology, is the OLDEST SCIENTIFIC DEPARTMENT OF THE GOVERNMENT OF INDIA. It was set up in 1767 and has evolved rich traditions over the years. Survey of India prepares the topographical maps in India for the entire country. Topographical maps under India and Adjacent Countries Series were prepared by the Survey of India till the coming into existence of Delhi Survey Conference in 1937. Henceforth, the preparation of maps for the adjoining countries was abandoned and the Survey of India confined itself to prepare and publish the topographical maps for India as per the specifications laid down for the International Map Series of the World.

3. Explain what is meant by 'map interpretation' and what procedure is followed for its interpretation.

Ans. Map interpretation involves the study of factors that explain the causal relationship among several features shown on the map. For example, the distribution of natural vegetation and cultivated land can be better understood against the background of land form and drainage. Likewise, the distribution of settlements can be examined in association with the levels of transport network system and the nature of topography.
Deriving accurate meanings from maps is called map interpretation. Knowledge of map language and sense of direction are essential in reading and interpreting topo-sheets. We must first look for the north line and the scale of the map and orient ourselves accordingly. We must have a thorough knowledge of the legends I key given in the map depicting various features. All topo-sheets contain a table showing conventional signs and symbols used in the map. We must be acquainted with conventional symbols, signs and colours.
The following procedure is followed in map interpretation:
(a) Finding from the index number of the topographical sheet, the location of the area in India. This would give an idea of the general characteristics of the major and minor physiographic divisions of the area.
(b) Find the scale of the map and the contour interval, which will give the extent and general land form of the area.
(c) Find the following features on tracing sheets.
(i) Major land forms - as shown by contours and other graphical features.
(ii) Drainage and water features - the main river and its important tributaries. (iii) Land use - i.e. forest, agricultural land, wastes, sanctuary, park, school, etc. (iv) Settlement and Transport pattern.
(d) Explain the distributional pattern of each of the features separately drawing attention to the most important aspect.
(e) Superimpose pairs of these maps and note down the relationship, if any, between the two patterns. For example, if a contour map is superimposed over a land use map, it provides the relationship between the degree of slope and the type of the land used.
(f) Aerial photographs and satellite images of the same area and of the same scale can also be compared with the topographical map to update the information.

4. If you are interpreting the cultural features from a topographical sheet, what information would you like to seek and how would you derive this information? Discuss with the help of suitable examples.

Ans. Cultural features are those which have been made by humans. Settlements, buildings, roads and railways are important cultural features shown on topographical sheets through conventional signs, symbols and colours. The location and pattern of distribution of different features help in understanding the area shown on the map. Distribution of Settlements can be seen in the map through its site, location pattern, alignment and density. The nature and causes of various settlement patterns may be clearly understood by comparing the settlement map with the contour map. Transport And Communication Pattern Relief, population, size and resource development pattern of an area directly influence the means of transport and communication and their density. These are depicted through conventional sings and symbols. Means of transport and communication provide useful information about the area shown on the map.
Settlements, occupation, means of communication and transportation, land use pattern are some of the culture features which are shown on topographical sheet using conventional sings, colours and symbols. We need to collect information for all of these Survey of India. The means of transportation include national or state highways, district roads, cart tracks, camel tracks, footpaths, railways, waterways, major communication lines, post offices, etc. Settlements are studied under the two heads: Rural Settlements and Urban Settlements.
The general occupation of the people of the area may be identified with the help of land use and the type of settlement. For example, in rural areas the main occupation of majority of the people is agriculture; in tribal regions, lumbering and primitive agriculture dominates and in coastal areas, fishing is practised. Similarly, in cities and towns, services and business appear to be the major occupations of the people.