Units of area parameter in ngspice
The units of "area" can depend upon the device.  For diodes it is the physical area, for MOSFets it can also be M or the scaling factor.  This is because in MOSfets the L and W can be used to calculate the drain and source areas (or you can give AS and AD in square meters directly - Si units), so M is used to scale for # of parallel devices when areas are not given directly.