def determine_subblock_lonlat(subblock):
    """
    calculates coordinates of the center of a subblock based on block_id and subblock_id
    :type subblock: (int, int)       x and y ids of small block subblock
    :rtype        : [float, float]   longitude and latitude of the small block center
    """
    corner = (-74.25, 40.5)
    return [corner[i]+(subblock[i]+0.5)*0.00025 for i in range(2)]