Choose the most appropriate answer: on a weather map, lines joining places that have the same temperature at a given time are called what?

Introduction / Context:
Weather maps and climate charts often use special lines to show patterns such as temperature, pressure and rainfall across a region. Understanding the names of these lines helps in reading meteorological information correctly. This question focuses on the term used for lines connecting places with equal temperature values at a given time or for a given period.

Given Data / Assumptions:

• Several different iso lines exist in geography and meteorology.
• Temperature, pressure and rainfall each have their own standard iso line names.
• We assume the map is showing air temperature measured at many stations.
• The question specifies equal temperature as the key variable.

Concept / Approach:
The prefix iso means equal. In meteorology, isotherms are lines drawn on a map that connect places with the same temperature. Isobars are lines connecting places with equal atmospheric pressure. Isohyets connect places with equal rainfall. Isomers is a term used in chemistry to describe compounds with the same molecular formula but different structures, not map lines. Therefore, the correct term for lines of equal temperature is isotherms.

Step-by-Step Solution:
Step 1: Identify that the question is about equal temperature on a map. Step 2: Recall that isotherms are defined as lines of equal temperature. Step 3: Recognise that isobars are lines of equal pressure and isohyets are lines of equal rainfall. Step 4: Note that isomers is unrelated and used in organic chemistry, not in cartography. Step 5: Select isotherms as the correct name of lines joining places with equal temperature.

Verification / Alternative check:
Geography and meteorology textbooks show weather maps where isotherms are drawn to show patterns of warm and cold regions. These maps help forecasters identify fronts and temperature gradients. Similarly, isobars on the same maps show pressure patterns that indicate high and low pressure systems. This consistent use across sources confirms that isotherms is the correct term for lines of equal temperature.

Why Other Options Are Wrong:
Option b, isohyets, refers to lines connecting places with equal rainfall for a specific period, often used in climatology rather than temperature mapping.

Option c, isomers, describes molecules in chemistry and has nothing to do with geographic maps or temperature.

Option d, isobars, denotes lines joining points with equal atmospheric pressure, not temperature, and is used mainly in weather forecasting for pressure systems.

Common Pitfalls:
Because all these terms begin with iso, students sometimes mix them up. A useful trick is to remember therm for temperature, bar for pressure and hyet for rainfall. Combining these roots with iso gives the correct meanings for isotherms, isobars and isohyets. Careful attention to the second part of the word avoids confusion in exams.

Final Answer:
Lines joining places of equal temperature are called Isotherms.