We have studied how first-year university science students construct graphs based on hypothetical qualitative physics scenarios. We gave students a questionnaire that asked them to complete two Cartesian graphs in one of three different scenarios (a ball rolling down a track, a beaker being filled with water, the resistance between different points on a metal bar) given as a written piece of text accompanied by a diagram of a hypothetical experiment that included three evenly spaced points on the set-up. Two of the three points were also indicated on the position axis of the partially drawn graph. We found that students can find it hard to translate equal spatial intervals in the experiment to a line graph. We found that most students either did not explain why they put the third point on the graph where they did, or did not plot the point at all. Some students drew unequal intervals on the position axis to indicate unequal time or resistance intervals. The difficulties became more prevalent as the levels of abstraction increased. Our findings suggest that constructing a scale on a qualitative graph requires significant mental effort from the students.