On a synoptic weather map, what does an isobar represent?

Concept overview / definition Weather maps often show families of curved lines that help visualise the pattern of pressure over large areas. These lines, called isobars, are drawn to connect locations where the atmospheric pressure has the same value when reduced to a common reference level. By examining the spacing and shape of isobars, meteorologists infer pressure centres and gradients that control wind patterns.

Why the correct option is correct The correct option captures the key idea that an isobar is a line joining places with equal pressure. In the transcript, the teacher explicitly states that these lines are known as isobars and defines them as lines joining places having the same pressure. In practice, pressures are usually adjusted to mean sea level or another standard level before drawing the isobars, so that differences reflect real horizontal variations rather than simple height effects.

Why the other options are incorrect Option B refers to temperature, which is mapped using isotherms, not isobars. Option C mentions equal rainfall, which would be shown by isohyets, and Option D describes equal wind speed, which is represented by isotachs. None of these alternatives matches the specific definition given for isobars in the discussion on pressure maps, so they must be rejected when applying basic climatological terminology.

UPSC exam tip / common confusion In prelims, similar sounding terms like isobar, isotherm, isohyet and isotach are often mixed deliberately. A quick memory aid is to link bar with pressure, therm with temperature, hyet with rainfall and tach with speed. When you see a map with lines labelled accordingly, first identify what quantity is being kept equal along each line and then match it to the correct term. This approach helps you avoid mistakes in simple definition-based questions that you should otherwise get right.