CDS (I) 2020 General Knowledge · Question 40 of 120

Correct — C, physiological density. Human geography uses three density measures off the same population figure, and they differ only in what goes in the denominator. Arithmetic density divides total population by total land area. Physiological density divides total population by the area of arable land — exactly the ratio the stem describes. Agricultural density divides the farming or rural population by the area of arable land. The point of the second measure is that it says something the first cannot: two countries can share an arithmetic density and be nothing alike if one is mostly cultivable and the other mostly desert or mountain. Egypt is the standard illustration, with a modest arithmetic density and an enormous physiological one, because almost the whole population is packed onto the Nile's floodplain.

• (a)agricultural density — Same denominator, different numerator. Agricultural density counts only the rural or farming population against arable land, so it measures how many cultivators a unit of farmland carries — a labour measure, not a population-pressure measure.
• (b)arithmetic density — The plain persons-per-square-kilometre figure, computed on total land area whether or not it can be farmed. It is the one quoted in census tables, and it is precisely the measure physiological density was devised to improve on.
• (d)economic density — Not a member of this standard triad at all. The word economic is doing no work here beyond sounding plausible next to three real terms.

Population density is a ratio, and the geography of a place lives in the denominator. Total area gives arithmetic density; arable area gives physiological density; pairing arable area with the farming population alone gives agricultural density. Reading the three together tells you not just how crowded a country is but how crowded it is relative to the land that can feed it, and how much labour that land absorbs.

This is a definitions item, so the trap is a near-synonym rather than a fact. Agricultural density is the one that catches people, because it also uses arable land, and the only difference is whether the numerator is everybody or only the farmers. Read the stem's numerator first — 'the number of people', not 'the number of farmers' — and the choice closes. India's arithmetic density at the 2011 Census was 382 persons per square kilometre; because a little under half the country's area is under cultivation, its physiological density is well above that.

• Arithmetic density is total population divided by total land area.
• Physiological density is total population divided by the area of arable land.
• Agricultural density is the rural or farming population divided by the area of arable land.
• Physiological density is the better measure of pressure on food-producing land, which is why Egypt's is extreme while its arithmetic density is unremarkable.
• India's arithmetic population density at the 2011 Census was 382 persons per square kilometre.

• Confusing physiological with agricultural density; both use arable land, but only one counts the whole population.
• Treating a low arithmetic density as evidence of spare capacity in a country that is mostly desert or high mountain.

As a straight definition, or as a comparison item asking which measure best shows pressure on cultivable land.

• practice — not a real PYQ

  The ratio of the farming population to the area of arable land is known as

  • (a)arithmetic density
  • (b)physiological density
  • (c)agricultural density
  • (d)gross density

  Answer(c) agricultural density — it counts only the cultivating population against farmland, and so measures labour pressure on the land.

• practice — not a real PYQ

  A country with a low arithmetic density but a very high physiological density is best described as one that

  • (a)has a large area of which only a small part is cultivable
  • (b)has a small area almost all of which is cultivable
  • (c)has very few farmers relative to its population
  • (d)has a rapidly falling birth rate

  Answer(a) has a large area of which only a small part is cultivable — Egypt is the textbook case, with the population concentrated on the Nile floodplain.