  We propose "aquanims" as new design metaphors for animated transitions that
preserve displayed areas during the transformation. Animated transitions are
used to facilitate understanding of graphical transformations between different
visualizations. Area is key information to preserve during filtering or
ordering transitions of area-based charts like bar charts, histograms,
treemaps, or mosaic plots. As liquids are incompressible fluids, we use a
hydraulic metaphor to convey the sense of area preservation during animated
transitions: in aquanims, graphical objects can change shape, position, color,
and even connectedness but not displayed area, as for a liquid contained in a
transparent vessel or transferred between such vessels communicating through
hidden pipes. We present various aquanims for product plots like bar charts and
histograms to accommodate changes in data, in the ordering of bars or in a
number of bins, and to provide animated tips. We also consider confusion
matrices visualized as fluctuation diagrams and mosaic plots, and show how
aquanims can be used to ease the understanding of different classification
errors of real data.
