def draw_squares(points, ax, width, col, lw=2):
    """ Given (y,x) centroid coordinates, draws on a given Matplotlib ax, squares of given width.

    Parameters
    ----------
    points : numpy array or list
        an array of (y,x) coordinates for plotting
    ax : Matplotlib figure axes instance
        e.g. from fig, ax = plt.subplots()
    width : int
        width of the square
    col : string
        a valid Matplotlib colour string or valid RGBA float values
    lw : int 
        line thickness of square
    
    Returns
    -------
    Nothing 

    """
    for p in points:
        y,x = p
        x1 = x - width/2.
        x2 = x1+ width
        y1 = y-width/2.
        y2 = y1 + width
        ax.plot([x1,x2,x2,x1,x1], [y1,y1,y2,y2,y1], color=col, lw=lw)
        
    return []