Currently, timeUnitBandPosition = 0.5 by default for bar and rect, but timeUnitBandPosition = 0 for all other marks, mainly because we previously did not support other timeUnitBandPosition. However, this pending PR allows us to adjust bandPosition for bars, and center align bars with ticks.

There are two reasons we should consider doing this:

1. More readable time binned axes

With bandPosition = 0.5 (current default)

(Spec)

Readers need to know that the bar for year 2011 is on the right of the bars.

However, with bandPosition = 0, we don't have this confusion.

2. Better Alignment for combo chart by default

It's a bit weird that lines and bars do not align by default, like in this example:

Spec

We need to either (a) set bar's bandPosition = 0

or (b) line's bandPosition = 0.5

(If we set bar's bandPosition to be 0 then we don't have this issue.