The authors investigated the effects of visual properties of hierarchical graphs on speed of comprehension: planarity (crossing of lines), slopes (orientation of lines), and levels (adjustment of dots). In each of 4 experiments, 30 participants responded to interpretive questions that required comparisons among the elements of the graph. Knowledge provided to participants differed across Experiments 1a, 1b, and 1c; question demands varied in Experiment 2. Analysis of response latencies showed that crossing of lines is the most influential variable independent of orientation, dot adjustment, and question demands. Speed of comprehension decreased with increasing question demands. When question demands were high, orientation of lines also had an effect on speed of comprehension. Preliminary conclusions for the presentation of hierarchical graphs are drawn.