Eddie,
In case of multiseries column charts, columns get distributed across the actual value i.e. in case of 2 dataSeries, 1st column will occupy space towards left of the actual value and the 2nd column towards right of it so that both becomes visible.
You can show just positive values by setting minimum to some negative value instead of setting it to 0, setting it to negative value adds some padding making 1st column visible.
—
Vishwas R
Team CanvasJS