How many latitudes are there on the globe drawn at 1 degree interval?

Question

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Correct — C, 179. Count the circles, not the degrees. Start at the Equator and step north one degree at a time: you can draw parallels at 1° N, 2° N and so on up to 89° N, which is 89 circles. Do the same southward for another 89. Add the Equator itself, which is the 0° parallel and a line in its own right. 89 + 89 + 1 = 179. The two remaining values of latitude, 90° N and 90° S, are the poles, and a pole is a single point — the place where the Earth's axis meets the surface. A parallel of latitude is by definition a circle running round the globe at a constant angular distance from the Equator, and at 90° that circle has shrunk to zero radius, so there is nothing left to draw. This is not a quibble invented for an exam. It is the same geometry that makes the length of a parallel 2πR cos φ: about 40,075 km at the Equator, roughly 20,000 km at 60°, and exactly zero at 90°. The same reasoning disposes of the two rival numbers. 178 is what you get by adding the hemispheres and forgetting that the Equator is a parallel. 180 is the angular span from 90° N to 90° S expressed in degrees — a measurement of arc, not a count of lines drawn along it — and no consistent counting rule produces it: admit the poles and you reach 181, exclude them and you reach 179, but never 180. It is worth knowing what one of those 179 lines is worth on the ground, because that is what the rest of the syllabus does with them. Work on the WGS84 ellipsoid that modern Indian surveying uses — equatorial radius 6,378,137 m exactly, flattening 1/298.257223563 — and one degree of latitude comes out at 110.574 km at the Equator and 111.694 km at the poles. It is longer near the poles, not shorter, because the Earth is flattened there and the meridian curves less sharply, so you must travel further to turn through the same one degree. The 179 parallels therefore step down a pole-to-pole meridian of about 20,004 km at intervals of roughly 111 km. Two working units were built on that step. The metre was defined by the French Academy of Sciences in 1791 as one ten-millionth of the distance from the North Pole to the Equator along the Paris meridian — the modern value of that quadrant is 10,002 km, which is how close an eighteenth-century survey came. And one minute of latitude is the nautical mile, fixed at exactly 1,852 metres by the International Extraordinary Hydrographic Conference at Monaco in 1929; the true arc of one minute at 45° latitude works out to 1,852.2 m. One honest caveat, because this answer is ours and carries medium rather than high confidence. 179 is the count used in standard Indian textbook practice, and it is plainly what the paper is testing. A minority of sources do count 181 by admitting the two poles as degenerate parallels, and a candidate holding that convention would have to choose (d). There is no Commission key for the 69th to settle the point; we follow the standard count.

Why the other options are wrong — (a) The distance from 90° N to 90° S is 180 degrees, and that is the figure being recalled here — but an angular span is not a count of the circles drawn along it. No convention yields 180: include the poles and the total is 181, exclude them and it is 179. This is the most tempting option precisely because 180 feels like the natural round answer for a hemisphere-to-hemisphere sweep.  (b) 89 north plus 89 south, with the Equator dropped. The Equator is 0° latitude and is itself a parallel — indeed the only one that is a great circle — so it has to be in the count. This is a slip rather than a misconception, and the quick guard against it is that the answer must be an odd number: a set symmetric about the Equator, with one member lying exactly on the axis of symmetry, can never total an even figure.  (d) This is only right under the minority convention that treats the two poles as parallels, which would give 181 and put the true value outside the list. Under the count used in Indian geography teaching — and the one the paper is testing — 179 is on offer, so the escape option is not needed. Choosing it means backing an alternative convention against the standard one.

Concept: A globe is ruled by two families of lines that together form the graticule. Parallels of latitude run east–west, measure angular distance north or south of the Equator, extend from 0° to 90° in each hemisphere and never meet. Meridians of longitude run north–south, measure angular distance east or west of the prime meridian at Greenwich, extend 0° to 180° each way, and all of them converge at the two poles. The asymmetry between the two families is exactly what this question tests. Every meridian is half of a great circle — a circle whose plane passes through the centre of the Earth — so any two opposite meridians together make one complete great circle. Among parallels, only the Equator is a great circle; every other parallel is a small circle whose radius falls off with the cosine of the latitude until, at 90°, it vanishes to a point. That is why a 1° graticule carries 179 parallels but 360 meridians, and why 90° N and 90° S are the only two latitude values that cannot be drawn as lines at all. One further distinction is the source of every disagreement about the count: a latitude is an angular coordinate, a parallel is a drawn circle. There are 181 whole-degree values of latitude from 90° S to 90° N inclusive; only 179 of them can be drawn.

State PCS 2023 Q96 — Geography PYQ with Answer

State PCS 2023 Q96 — Geography PYQ with Answer