A WetBase with a centre drain has the drain aperture located midway between both the long and short edges.
With an offset drain the drain aperture is located in the centre of the width or short edge of the base but is 450mm from one end of the base. The choice between an offset or centre drain is often determined by the need to avoid joists and/or to have the drain immediately below a shower head.
Please see the WetBaseplan diagrams in the product descriptions for the exact location of the drain in each WetBasesize.