Problem 1
- Test level
- Multiple choice
- No calculator
- 4 pts
The isoline map shows mean annual rainfall on the fictional island of Orlund, with an isoline every 200 mm. Points P and Q lie 20 km apart on an east-west line. Points R and S also lie 20 km apart on the same line, farther east. Which conclusion is best supported by the map?
Answer
Rainfall changes much faster per kilometer between P and Q than between R and S: the line between P and Q crosses three isolines, while the line between R and S crosses none.
Full solution
On an isoline map, how close together the lines are shows how steeply the value changes. Closely spaced lines mean a steep change.
Count the isolines crossed on each 20 km stretch. Going east from P to Q you cross the 1200, 1000 and 800 mm lines. Between R and S you cross none (both lie in the band between 200 and 400 mm).
Three isolines at 200 mm intervals means a change of at least 400 mm and less than 800 mm over 20 km between P and Q, against less than 200 mm between R and S. So the change is much faster between P and Q.
Check each distractor. (B) mixes up wide spacing with heavy rain; wide spacing means a gradual change, and R and S are in the driest band. (C) claims an exact value that the map cannot give. (D) reads the number of rainy days from a total; isolines show amounts, not how often it rains. (E) reverses the comparison.
Where students lose points
Reading wide spacing between isolines as high values. Spacing shows the steepness of change, and the numbers on the lines show whether the values are high or low.

