def cell_size(layout):
    """
    Determine the geodetic dimensions of a pixel in a tile of a given layout

    Args:
        layout (gps.LayoutDefinition)

    Returns:
        (float, float) tuple
    """
    ex = layout.extent
    w = float(abs(ex.xmax - ex.xmin))
    h = float(abs(ex.ymax - ex.ymin))
    tl = layout.tileLayout
    return (w / (tl.layoutCols * tl.tileCols), h / (tl.layoutRows * tl.tileRows))