The Chartroom was made about twice the size of the original in order to be able to properly film in that space. Many of the sets were made larger than what they actually were in order to be able to film the space with all four walls intact, and not the standard 3-wall setup. While Cameron's sets were very faithful, the scale was somewhat exaggerated to make things appear grander (such as the grand staircase)
I think the room that you are referring (just to be technical) to is called the “Navigation Room’’. The Chart room was located behind the Wheelhouse next to another small room, the Pilot Room. This was at first only a Titanic feature, but then was later arranged on the Olympic after her 1913 refit. The Chart room, I think was where Boxhall posted the iceberg warnings on a notice board. In reality, the Navigation room as Robert said was very small and it had only a side table with drawers and a couch.