The same constant tendency which exists among abutting owners to encroach on the street lines, exists among shore owners to encroach on the beds of navigable waters. Hence it is necessary to establish what are known as harbor lines, settling a point beyond which solid fillings cannot be put (i. e., bulkhead lines), nor platforms nor piers built (i. e., pierhead lines). These lines are now established by the Federal Government, but were formerly laid down in some instances by the city and some by the State. In 1857 a harbor commission laid out a general set of lines for the port of New York as it then existed. Moreover, plans for improvements, even of private property, have to be passed upon by the authorities. All of this should be carefully borne in mind by prospective purchasers of water-front property, particularly of land under water.