Such a surface is most commonly the phase boundary. The surface of the corn field at a height where the stalks reach, can considered as very accurate approximation of the phase interface.
Uso vile ni wengi kawaida mpaka awamu. uso wa shamba nafaka katika urefu ambapo mabua kufikia, unaweza Anachukuliwa kama makadirio sahihi sana ya interface awamu.