Step 1: Convert each representative fraction to a decimal value. $1{:}1000 = 0.001$, $1{:}5000 = 0.0002$, $1{:}50000 = 0.00002$, $1{:}100000 = 0.00001$. Step 2: Recall that a numerically larger RF value means a larger map scale. A large scale map means the fraction $\frac{1}{n}$ itself is numerically larger (n smaller), and a small scale map means the fraction is numerically smaller (n larger). Ranking the four values: $0.001 > 0.0002 \gg 0.00002 > 0.00001$. Step 3: Group the two largest and two smallest values. P (0.001) and Q (0.0002) are the two largest fractions, so they belong to the large-scale group. R (0.00002) and S (0.00001) are the two smallest fractions, so they belong to the small-scale group. This also matches practical usage: 1:1000/1:5000 maps show plot or building-level detail (cadastral/engineering plans), while 1:50000/1:100000 maps are regional topographic sheets, which is the everyday sense of large (very detailed, small area) versus small (less detailed, large area) scale. Step 4: State the grouping. [P, Q] are large scale and [R, S] are small scale, matching option (A).\[ \boxed{\text{[P, Q] large scale; [R, S] small scale}} \]
