The location, in this vast low delta and coastal plain, of the system of canals already described, is indicated by the two rectangles in the south-east corner of the sketch map, Fig. 53. The heavy barred black line extending from Hangchow in the south to Tientsin in the north represents the Grand Canal which has a length of more than eight hundred miles. The plain, east of this canal, as far north as the mouth of the Hwang ho in 1852, is canalized much as is the area shown in Fig. 52. So, too, is a large area both sides of the present mouth of the same river in Shantung and Chihli, between the canal and the coast. Westward, up the Yangtse valley, the provinces of Anhwei, Kiangsi, Hunan and Hupeh have very extensive canalized tracts, probably exceeding 28,000 square miles in area, and Figs. 54 and 55 are two views in this more western region. Still further west, in Szechwan province, is the Chengtu plain, thirty by seventy miles, with what has been called "the most remarkable irrigation system in China." Westward beyond the limits of the sketch map, up the Hwang ho valley, there is a reach of 125 miles of irrigated lands about Ninghaifu, and others still farther west, at Lanchowfu and at Suchow where the river has attained an elevation of 5,000 feet, in Kansu province; and there is still to be named the great Canton delta region. A conservative estimate would place the miles of canals and leveed rivers in China, Korea and Japan equal to eight times the number represented in Fig. 52. Fully 200,000 miles in all. Forty canals across the United States from east to west and sixty from north to south would not equal, in number of miles those in these three countries today. Indeed, it is probable that this estimate is not too large for China alone. As adjuncts to these vast canalization works there have been enormous amounts of embankment, dike and levee construction. More than three hundred miles of sea wall alone exist in the area covered by the sketch map, Fig. 52. The east bank of the Grand Canal, between Yangchow and Hwaianfu, is itself a great levee, holding back the waters to the west above the eastern plain, diverting them south, into the Yangtse kiang. But it is also provided with spillways for use in times of excessive flood, permitting waters to discharge eastward. Such excess waters however are controlled by another dike with canal along its west side, some forty miles to the east, impounding the water in a series of large lakes until it may gradually drain away. This area is seen in Fig. 53, north of the Yangtse river.