The Detailed Position of Commercial far we have been considering the geographical conditions which cause commercial centers of a particular character or stage of development to be located in certain general types of regions. Now we must consider why the centers are located in particular positions within their general regions and why one position fosters growth far more than another. The main factor here is transportation. A city whose main business is commerce must be so placed that it is the natural catch basin for the produce of surrounding regions. Trade must flow to it more easily than to any neighboring center. The larger the natural catch basin, the larger the commercial center. Such basins are usually easy to locate on a relief map because they are primarily the natural drainage basins, for man utilizes nature's routes wherever possible, either floating goods down stream or building roads in the valley bottoms. New York City is a famous example of a commercial city which owes much of its supremacy over such neighbors as Philadelphia, Providence, and Boston to the Hudson-Mohawk Valley, which penetrates the Appalachian high land, thus giving easy access to the vast level region extending as far as the Rocky Mountains. St. Louis and New Orleans are other examples of commercial centers whose position depends on the relation of trade routes to river basins. They cannot rival New York and Chicago because their main routes run southward instead of eastward toward the most active regions of the United States and Europe.
The physical conditions which determine the position of a com mercial center may be briefly summed up as follows: (1) Junctions of valleys, which usually means of rivers, as at Pittsburgh. (2) Crossing places of roads in a plain. Generally a plain contains many crossings since the roads and railroads can go almost everywhere. Hence, there are usually many small commercial centers as in Iowa and Indiana, but the greatest combination of cross roads may cause one city to out rival the others as Indianapolis has (lone. (3) Mountain gaps. Many trade routes are temporarily dammed as it were by meeting the moun tains, and hence have to turn and flow parallel to the mountains until they find a gap as at Vienna. (4) Breaks in inland water routes also determine the position of a city as in the case of the falls of the Ohio where Louisville grew up. (5) The crossing places of rivers determine the location of a large number of cities among which are St. Louis and Omaha. The number of cities whose names contain the syllables " bridge " or " ford," or their foreign equivalents testifies to the great importance of this cause which determined the original position of many great cities including London and Paris. (6) The heads and to a less extent any main indentations of lakes, and the places where lakes meet land routes are favorable for the growth of commercial centers. Buf
falo, Chicago, and Duluth are examples. (7) Closely allied to the lake centers of commerce are cities like Albany at the head of deep water navigation. Such places, like most of those where land and water meet, owe much of their importance to the fact that the means of trans portation must be changed. The cargo must be transferred from ocean vessels to canal boats, railways, or trucks.
(8) Last and most important are the places where land routes meet ocean routes. Their importance is due to the extreme cheapness and ease of water transportation, and to the fact that when goods are once on the water they can be carried immense distances and in a great many directions without transshipment. Today, the oceans, instead of being barriers to commerce, may almost be called magnets. The Atlantic draws the United States into intimate contact with Europe and make us share its problems whether we will or no. And the Pacific draws us toward Japan and China so that we cannot ignore what happens in those countries. Commerce thinks of the ocean as a great level track with infinite switching possibilities and requiring far less fuel than even the best railway.
Ocean ports may be divided into four types according to the char acter of the harbor and its relation to routes on the land: (A) Open roadsteads such as Boulogne. These are usually poor because they do not offer good, safe harbors with plenty of depth and protection from the winds and waves. Also they are rarely located at the mouths of large valleys so that transportation toward the interior is hampered. (B) Bay ports like Boston. At such places the harbor may be safe, commodious, and deeper than that of Boston, and there may be plenty of room for docks and for a city, but if they are like Boston in lack ing a gentle, easy valley leading far into the interior, they are much hampered. If the Hudson Valley ran eastward instead of southward from Albany, Boston rather than New York might be America's greatest city. (C) River ports like New Orleans and Antwerp have the advan tage of easy communication inland, but they are often hampered by lack of depth and of space for anchorage, docks and wharves. Only by extensive digging or by going far up or down the river can room be found. (D) Ports with both a bay and a river, as at New York and San Francisco, are the most fortunate of all. They usually combine safe and commodious anchorage with plenty of room for clocks and wharves and with easy access to the interior. Nevertheless, they do not necessarily determine the positions of the largest cities, for Riga and Nikolaiyevsk at the mouth of the Amur have such positions. So, too, does Smyrna, but it cannot rival Boston for example.