def METHOD_NAME(ZeroMap,sizeinmetres):
    """
    Determine cellength. Always returns the length
    in meters.
    """
    if sizeinmetres:
            reallength = celllength()
            xl = celllength()
            yl = celllength()
    else:
        aa = ycoordinate(boolean(cover(ZeroMap + 1,1)))
        yl, xl = lattometres(aa)
        xl = xl * celllength()
        yl = yl * celllength()
        # Average length for surface area calculations.
        reallength = (xl + yl) * 0.5
    return xl,yl,reallength