The treemap layout can now be set to "sticky" mode, which preserves the row
arrangements from an earlier layout. This is particularly handy for animating
treemaps, as it avoids the temporary occlusion as nodes swap positions. Thanks
to @philogb and the New York Times for the inspiration!
Still a work in progress. Need to decide on the appropriate API for representing
tree structures; not sure I want to go the heavyweight pv.dom route. May also
need rounding to exact pixel values.
Michael Bostock