To get my simple mind to understand it.... the way I have to picture it my head is...

in 2D sonar there is a conical downward looking sonar that the processor turns "sideways" to show the image on the screen...

in Di sonar there is a thin slice sideways looking sonar that the processor leaves sideways to show the image on the screen...the processor just changes the color of the pixels (and with more detail because of the Si element being used)...