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Modern Business Geography 
more, mud or sand must often be dredged from the harbor floor. 
Dredgers are at work all the time at Philadelphia, New York, 
Boston, and many other ports. There must also be ample room; 
for vessels to turn about and to swing at anchor. For this 
reason ledges in the midst of harbors are often blasted away, as 
at New York. Too deep a harbor, however, is bad, because 
it does not afford anchorage. 
Convenient space for docks, warehouses, and other buildings 
is likewise necessary. On the edge of the water there must be 
level land on which warehouses and other buildings can be 
erected. The harbor of Baltimore is fortunate in this respect. 
[n such places as Boston, Buenos Aires, and Manila, where 
dredging has been carried on to make places for docks, the mud 
and sand dredged from the bottom have been used to fill up 
the shallow parts of the bay close to the land. 
A good harbor is free from ice. Since ships cannot move freely 
in the ice, harbors like those of Montreal and Riga must often 
be kept open by ice-breakers. No ports in the United States 
suffer much in this respect. 
How a prosperous hinterland helps a seaport to grow. Even 
though a harbor is excellent and is the meeting place of many inland 
routes, a great city will grow up only if these routes penetrate a region 
which is prosperous. In that case the city collects abundant products 
of the fields, forests, mines, or factories of the interior and exchanges 
them for the goods of other regions. The region from which a city 
receives goods for exchange with other parts of the world is called its 
hinterland; Baltimore, for example, owes much of its growth and wealth 
to the fact that the land that lies behind (hinfer) it is extensive and 
productive. 
THE SEAPORTS OF THE UNITED STATES 
Transportation by water is so important that the majority of the 
world’s great cities are located on waterways. In the United States 
more than one person out of every five lives in a port of some sort, 
either on the ocean, or on a lake or river. Of the people that live in 
cities with a population of more than 200,000, more than 12,000,000 
live in the thirteen largest seaports, nearly 6,000,000 in seven lake 
ports, and about 3,400,000 in eight river ports. On the other hand, 
only 1,200,000 lived in the five cities of more than 200.000 population 
which are not on waterways (page 330). 
The ocean ports of the United States are all located where harbors 
make it possible for ships to come close to the land in safety, and 
where valleys or plains permit easy access to the interior. In prac- 
tically all the ports, the harbors are bays or river mouths where