There used to be an option {transparent|solid} to this command. Now you get the same effect from `set grid {front|layerdefault}`, respectively.
The command `set pm3d map` is equivalent to `set pm3d at b`; `set view map`; pm3d; pm3d;. It is used for backwards compatibility, when `set view map` was not available. Take care that you properly use zrange and cbrange for input data point filtering and color range scaling, respectively; and also `set (no)surface` seems to have a (side?) effect.