Split from https://github.com/plotly/plotly.js/pull/3506#issuecomment-460696495 We don't currently match auto-binning for `histogram2d` traces on the same subplot, unlike we do for stacked & grouped `histogram` traces post https://github.com/plotly/plotly.js/pull/3044. To do so, we could either: - add a new attributes (e.g. `bingroup`), or - add "shared" `(x|y)bins` objects in the layout similar to "shared" color scales/axes discussed in https://github.com/plotly/plotly.js/issues/3431 cc @nicolaskruchten