Maps, Map Projections and Remote Sensing for Exams

The correct answer is A. The representative fraction is a pure ratio without units, so one unit of length on the map stands for fifty thousand of the same units on the ground; it can be read in centimetres, inches or any other unit, which is why it is understood everywhere. Option B is wrong because it mixes the units: one centimetre on such a sheet stands for fifty thousand centimetres, that is half a kilometre, not fifty thousand kilometres. Option C is wrong because the representative fraction says nothing about the area a sheet covers; that depends on the size of the paper. Option D is wrong because the fraction compares the map with the ground, not with a photograph, and a map may be drawn from a ground survey with no photograph involved at all.

The correct answer is A, 2 m. The contour interval chosen for a sheet depends chiefly on its scale and on the relief of the ground: a large-scale map can carry closely spaced contours without the lines running into each other, so a small interval is both possible and desirable. For a scale of one to ten thousand, which is a large scale used for detailed survey and engineering work, an interval of two metres is the usual choice. Options B, C and D are wrong because five, ten and twenty metre intervals belong to progressively smaller scales and flatter requirements of detail: an interval that large on a one to ten thousand sheet would leave the slopes almost blank and waste the accuracy the scale allows. The working rule to remember is that the smaller the scale and the rougher the country, the larger the contour interval.

The correct answer is B, cylindrical, and it preserves shape. Mercator's is a cylindrical projection on which both parallels and meridians are straight lines crossing at right angles, and it is orthomorphic or conformal, meaning that shapes are true locally and a rhumb line of constant bearing plots as a straight line. Option A is wrong on both counts: the projection is not conical, and it badly exaggerates area in the higher latitudes, which is the standard criticism of it. Option C is wrong because zenithal or azimuthal projections are drawn on a plane tangent to the globe and are used mainly for the polar regions, and Mercator's does not keep distances true. Option D is wrong because it combines the wrong family with a property the projection does not claim; its usefulness in navigation comes from bearings being preserved everywhere, not only at the poles.

The correct answer is B, rainfall. An isohyet joins points receiving the same amount of precipitation over a stated period, and rainfall maps of India are drawn with isohyets to mark the wet and dry belts. Option A is wrong because a line of equal temperature is an isotherm, used on temperature and climate maps. Option C is wrong because a line of equal atmospheric pressure is an isobar, the line on which weather maps are built and from which pressure gradients and winds are read. Option D is wrong because a line of equal duration of sunshine is an isohel, which is the pair most often confused with isohyet in examinations. Two more worth remembering are the isoneph for equal cloudiness and the isobath for equal depth of water.

The correct answer is B, a steep slope. Since the contour interval is constant on a sheet, the horizontal distance between two contours measures how far one must walk to rise by that fixed height; a short distance therefore means a rapid rise, that is a steep slope. Option A is wrong because a gentle slope shows the opposite pattern, with contours spread widely apart. Option C is wrong because a plain has very few contours at all, and those far apart, since there is little change in height. Option D is wrong because the flat top of a plateau is shown by widely spaced or absent contours, with closely spaced contours only along its steep edges or scarp. Contours that actually merge indicate a cliff or a vertical face, and a V pointing upstream marks a valley.

The correct answer is C, IRS-1A, 1988. It was the first satellite of the Indian Remote Sensing series and marked the beginning of operational earth observation for agriculture, forestry, water resources and land use in India. Option A is wrong because Aryabhata, launched in 1975, was India's first satellite and carried experiments in astronomy and physics, not an earth observation payload of the operational kind. Option B is wrong but close: Bhaskara-I of 1979 was India's first experimental earth observation satellite, and the word operational in the question is what separates it from IRS-1A. Option D is wrong because Cartosat-1, launched in 2005, came much later in the programme and was built for high-resolution cartographic mapping, by which time the Indian Remote Sensing series was long established.

The correct answer is C, RADAR. An active sensor generates its own energy, sends it to the target and measures what returns; RADAR does this with microwaves and LiDAR with a laser pulse, which is why such sensors can image at night and, in the case of microwaves, through cloud, haze and smoke. Option A is wrong because an aerial camera depends on sunlight falling on the ground and is therefore passive. Option B is wrong for the same reason: a multispectral scanner that records reflected sunlight supplies no energy of its own. Option D is wrong because a thermal sensor records the radiation the earth itself emits, which again is energy the sensor did not produce, so it is passive even though it can work at night. The dividing line is the source of the energy, not the time of day.

The correct answer is C, about 36,000 km above the equator. At that height a satellite's orbital period equals the period of the earth's rotation, so it stays above the same point on the equator and appears fixed in the sky, which is what communication and weather satellites need. Option A is wrong because a few hundred kilometres is the range of the near-polar sun-synchronous orbits used by earth observation satellites, which cross the equator at the same local time on each pass. Option B is wrong because at ten thousand kilometres the period is far shorter than a day and the satellite would drift across the sky. Option D is wrong because one lakh kilometres is well beyond the geostationary belt and the satellite's period would be much longer than a day.

The correct answer is B, Hyderabad. The National Remote Sensing Centre, a centre of the Indian Space Research Organisation, works from Hyderabad and operates the earth station at Shadnagar nearby, where data from Indian and foreign satellites is received. Option A is wrong because Bengaluru is the headquarters of ISRO itself and the location of the U. R. Rao Satellite Centre, where satellites are built. Option C is wrong because Ahmedabad is the home of the Space Applications Centre, which develops payloads and applications. Option D is wrong because Dehradun is the headquarters of the Survey of India, the topographical mapping agency, and also of the Indian Institute of Remote Sensing, which is a training and research institute rather than the data centre. Remember the three cities together: Bengaluru for ISRO headquarters, Ahmedabad for the Space Applications Centre and Hyderabad for the National Remote Sensing Centre, with Dehradun for the Survey of India.

The correct answer is D, spatial resolution. It is usually expressed as the ground size of one pixel, so a sensor of one metre resolution can separate objects about a metre across, which is what makes high-resolution imagery useful for urban mapping. Option A is wrong because spectral resolution refers to the number of wavelength bands recorded and how narrow each is, which decides how finely different materials can be told apart. Option B is wrong because radiometric resolution is the sensitivity of the sensor to differences in the strength of the signal, expressed in the number of levels or bits. Option C is wrong because temporal resolution is the interval after which the same area is imaged again, which matters for watching a crop grow or a flood spread. All four together describe the quality of a data set.

The correct answer is A. A cadastral map is a very large-scale map of a village or a town drawn to register plots, fields, their boundaries and their owners, and it is the basis of land revenue records and of the registration of property. Option B is wrong because a rainfall map is a thematic or distribution map, drawn on a small scale with isohyets. Option C is wrong because air routes appear on small-scale route or atlas maps, where detail of the ground is deliberately left out. Option D is wrong because relief is shown on topographical maps with contours, and the words small scale make it doubly wrong, since cadastral maps are the largest-scale maps in regular use. The word cadastre itself means a register of property, which is the easiest way to remember it.

The correct answer is B, homolographic. A homolographic or equal-area projection keeps the ratio of areas on the map the same as on the globe, which is why world distribution maps of population, crops or forests are drawn on projections such as Mollweide's or the sinusoidal. Option A is wrong because orthomorphic, also called conformal, describes a projection that keeps shapes true locally, as Mercator's does; no projection can be both orthomorphic and homolographic over a large area. Option C is wrong because azimuthal or zenithal names the family of projections drawn on a plane touching the globe, not the property preserved. Option D is wrong because the gnomonic is one particular perspective zenithal projection on which a great circle plots as a straight line, useful in aviation.