Question

Which instrument is used to measure a road, a rail line or a river on a map?
A) Nephoscope
B) Nephelometer
C) Vernier calliper
D) Opisometer

Answer 1

Hint: A map is a symbolic representation of a space that emphasises linkages between things, areas, or themes. Many maps are static, meaning they are set to paper or another lasting media, although others are dynamic and interactive.

Complete answer:
Let us look at the given options:
A) Nephoscope: This option is incorrect because a nephoscope was 19th-century equipment that used transit-time measurement to determine the altitude, direction, and velocity of clouds. It is not used to measure a road, a rail line or a river on a map.

B) Nephelometer: This option is incorrect because a nephelometer is not used to measure a road, a rail line or a river on a map. A nephelometer, also known as an aerosol photometer, is a device that measures the number of suspended particulates in a liquid or gas colloid.

C) Vernier calliper: This option is incorrect because the vernier scale is a visual aid that uses mechanical interpolation to take an accurate measurement reading between two graduation markings on a linear scale, thereby increasing resolution and minimising measurement uncertainty by reducing human estimation error. It is not used to measure a road, a rail line or a river on a map.

D) Opisometer: This is the correct answer. An opisometer is a device for measuring curved lines (such as those on a map) that consists mainly of a screw with a wheel-shaped nut that rotates forward along the curved lines and then backwards along a straight scale to its original position on the screw. The most typical application of the device is to measure the lengths of roads, rivers, and other line features on maps. It, also known as a curvimeter, heliograph, or map measurer, is a device that measures the lengths of curved lines of any shape.

Thus, the correct answer is Option (D) i.e, Opisometer.

Note: A simple opisometer is a handle with a toothed wheel with a known circumference. The wheel is run along the length of the curved line to be measured. While doing so, count the number of teeth and make a mark on the handle. The wheel is connected via gearing to a rotary dial from which the line length can be directly read in more advanced variants, also referred to as a chartometer.