Which of the following is an example of an active remote sensing sensor?

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.