Time-varying geospatial data presents some specific challenges for visualization. Here, we report the results of three experiments aiming at evaluating the relative efficiency of three existing visualization techniques for a class of such data. The class chosen was that of object movement, especially the movements of vehicles in a fictitious landscape. Two different tasks were also chosen. One was to predict where three vehicles will meet in the future given a visualization of their past movement history. The second task was to estimate the order in which four vehicles arrived at a specific place. Our results reveal that previous findings had generalized human perception in these situations and that large differences in user efficiency exist for a given task between different types of visualizations depicting the same data. Furthermore, our results are in line with earlier general findings on the nature of human perception of both object shape and scene changes. Finally, the need for new taxonomies of data and tasks based on results from perception research is discussed.

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type ; displacement, as specified above, of the overlarge La3+ from a central position is responsible for the expansion into the previously unheard of ten-coordination group. (How the substitution of smaller rare ions for La3+ can modify this configuration for the better is discussed in the accompanying communication.6) The nine-coordination group7 of D3h symmetry, the uniquely satisfactory choice8 for La3+ in unconstrained circumstances, is quite unadapted to meet the stereochemical requirements of the chelating agent.Of the four carboxylate oxygen atoms (Ou) which are not complexed by La3+, the one carrying the acid hydrogen can be identified from the bonding data which follow. (Standard deviations for individual bond lengths are 0.0030-0.0035 A. for La-Oc, La-OH2, and La-N; 0.004-0.006 A. for C-Oc and C-Ou.) The averaged length, with mean deviation, for three of the four La-Oc bonds is 2.537 (0.007) A., and the corresponding data for the associated C-Oc and C-Ou bonds are, respectively, 1.261 (0.008) and 1.249 (0.004) A.; this nearly trivial lengthening (0.012 A.

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