NCERT Solutions for Class 11 Geography (Practical Work in Geography) Introduction to Aerial Photographs [Old Book]

NCERT
SOLUTIONS
CLASS - 11th

aglase .co

Book : Practical Work in Geography Ncert Solutions | Chapter - 6 Social Science Geography

Class : 11th

Subject : Geography

Chapter : 6

Chapter Name : Introduction to Aerial Photographs

Q1 In which of the following aerial photographs the horizon appears?
a. Vertical
b. Near-vertical
c. Low-oblique
d. High-oblique

Answer. (b) Near-Vertical

Page : 83 , Block Name : Exercise

Q2 In which of the following aerial photographs the Nadir and the principle points
coincide?
a. Vertical
b. Near-vertical
c. Low-oblique
d. High-oblique

Answer. (a) Vertical

Page : 83 , Block Name : Exercise

Q3 Which type of the following projections is used in aerial photographs?
a. Parallel
b. Orthogonal
c. Central
d. None of the above.

Answer. (c ) Central

Page : 83 , Block Name : Exercise

Page 1 of 4

Book : Practical Work in Geography Ncert Solutions | Chapter - 6 Social Science Geography

Q1 State any three advantages that an aerial photograph offers over ground based
observations.

Answer. An aerial photograph offers the following advantages over ground based
observations:
● Aerial photography provides a bird’s eye view of large areas, enabling us to see
features of the earth's surface in their spatial context.
● An aerial photograph is a record of the surface features at an instance of
exposure. It can, therefore, be used as a historical record.
● The sensitivity of the film used in taking aerial photographs is relatively more than
the sensitivity of the human eyes.

Page : 83 , Block Name : Short Answer Questions

Q2 How is an aerial photograph taken?

Answer. An aerial photograph is taken using a high precision camera mounted on a
helicopter, aircraft or unmanned aerial vehicle.

Page : 83 , Block Name : Short Answer Questions

Q3 Present a concise account of aerial photography in India.

Answer. Aerial photography in India goes back to 1920 when large-scale aerial
photographs of Agra city were obtained. Subsequently, Air Survey Party of the Survey
of India took up aerial survey of Irrawaddy Delta forests, which was completed during
1923–24. Subsequently, several similar surveys were carried out and advanced
methods of mapping from aerial photographs were used. Today, aerial photography in
India is carried out for the entire country under the overall supervision of the Directorate
of Air Survey (Survey of India) New Delhi. Three flying agencies, i.e. Indian Air Force,
Air Survey Company, Kolkata and National Remote Sensing Agency, Hyderabad have
been officially authorised to take aerial photographs in India.

Page : 83 , Block Name : Short Answer Questions

Q4 Answer the following questions in about 125 words :
i) What are the two major uses of an aerial photograph? Elaborate.
ii) What are the different methods of scale determination?

Page 2 of 4

Book : Practical Work in Geography Ncert Solutions | Chapter - 6 Social Science Geography

Answer.

(i) The two major uses of an aerial photograph are :
● Photogrammetry : It refers to the science and technology of making reliable
measurements from aerial photographs. The principles used in photogrammetry
facilitate precise measurements related to the length, breadth and height from
such photographs. Hence, they are used as the data source for creating and
updating topographic maps.
● Image Interpretation : It is an art of identifying images of objects and judging their
relative significance. The principles of image interpretation are applied to obtain
qualitative information from the aerial photographs such as land use/land cover,
topographical forms, soil types, etc. A trained interpreter can thus utilise aerial
photographs to analyse the land-use changes.

(ii) The different methods of scale determination are as follows :
● By Establishing Relationship Between Photo Distance and Ground Distance : If
additional information like ground distances of two identifiable points in an aerial
photograph is available, it is fairly simple to work out the scale of a vertical
photograph. Provided that the corresponding ground distances (D​g ) are known
for which the distances on an aerial photograph (D​p​) are measured. In such
cases, the scale of an aerial photograph will be measured as a ratio of the two,
i.e. D​p​/ D​g​.
● By Establishing Relationship Between Photo Distance and Map Distance: As we
know, the distances between different points on the ground are not always
known. However, if a reliable map is available for the area shown on an aerial
photograph, it can be used to determine the photo scale. In other words, the
distances between two points identifiable both on a map and aerial photograph
enables us to compute the scale of the aerial photograph (S​p​). The relationship
between the two distances may be expressed as:

Photo scale : Map scale = Photo distance : Map distance

We can derive Photo scale (S​p​) = Photo distance (D​p​) : Map distance (D​m​) x Map
scale factor (msf)

● By Establishing Relationship Between Focal Length (f) and Flying Height (H) of
the Aircraft : If no additional information is available about the relative distances
on photograph and ground/map, we can determine the photo-scale provided the
information about the focal length of the camera (f) and the flying height of the

Page 3 of 4

Book : Practical Work in Geography Ncert Solutions | Chapter - 6 Social Science Geography

aircraft (H) are known (Figure below). The photo scale so determined could be
more reliable if the given aerial photograph is truly vertical or near vertical and
the terrain photographed is flat.
The Figure may be used to derive the photo-scale formula in the following way:
Focal Length (f) : Flying Height(H) = Photo distance (D​p​) : Ground distance (D​g​)

Page : 83 , Block Name : Exercise

Page 4 of 4