the modern large cities are the crossroads of the nation and the focal points of their respective geographic regions many factors operating singly or in combination influence the location and the growth of cities good harbors have been the determining factor in coastal cities on the atlantic coast on the gulf and on the pacific our coastal cities terminals of ocean trade routes on the great inland waterways mighty cities have sprung up throbbing with the commerce of their region rivers and lakes afford avenues for the flow of commerce urban centers often develop at the head of navigation or at other transfer points from one mode of transportation to another city's rose near mineral resources gold silver copper iron coal or petroleum often processing industry has followed the extraction industry and the mining town became a city  mildly even climate for leisure relaxation and convalescence consequently the climate has been the outstanding factor in the growth of certain cities during several decades following the birth of our nation there were only a few scattered seaport cities of more than twenty five thousand population then new urban centers in great numbers began to appear at strategic points in the wake of the westward movement the expansion and growth of cities has been marked by an accelerated tempo those urban communities that were favorably located with regard to trade and commerce domestic or foreign development in large cit today there are in the united states about four hundred cities of more than twenty five thousand population during several decades after the founding of the republic the nation was dominantly rural eight seven here represents one million people black and white for rural and solid black urban with the extension of industry and commerce young people in greater numbers from farms and villages sought their livelihood in cities and there were joined by the millions of immigrants although the united states is today predominantly urban the south and the west are still mainly rural urban people depend on farms for food modern farm machinery and scientific agriculture have greatly increased the agricultural production per man and thereby reduce the proportion of people is needed on farms cities have grown at different rates those that grew most rapidly possessed advantages which led to extensive business incomers great power sources also contributed to the development of cit river valleys through the appalachian mountains peppe the west by means of waterways highways and railroad coastal plains to the north east and south connect with new york by railroads here the products of a nation are exchanged for those of other lands to chicago flow the agricultural products of the western plains iron ore comes down the great lakes meeting the coal from illinois and in chicago is made into steel this connects bike and now reverend rail with the gulf of mexico and by water  of an area usually embraces a central city and it's densely populated surrounding regions specifically a metropolitan area is sometimes regarded as one which totals one hundred thousand people in a contiguous area with at least one hundred fifty people per square mile off in the metropolitan area straddles state and county boundaries it includes a maze of other political units cities villages and towns ships with much overlapping duplications and conflict of governmental functions pertaining to highways schools police protection water supply and taxation such metropolitan areas of more than one hundred thousand are found in all parts of the united states but they are most concentrated in the northeastern section of the country the center of the metropolitan area is utilized most intensively with closely spaced tall buildings the intensity of utilization decreases toward the outskirts as evidenced by lower buildings with more space between them stores next there is a transitional zone of warehouses terminals and old homes the third zone is occupied by moderately priced apartments the fourth zone has single family homes beyond the country homes and large in every large metropolitan area satellite cities have sprung up some of these are highly industrialized while others are mainly residential for those who work in the central city the entire lower mohawk valley is an industrialized metropolitan area with three central cities and several additional industrial centers the high value of land in the city leads to crowded skyscrapers and people are compelled to live in crowded quarters while opportunities for recreation and healthful living are limited electric power a contribution of modern technology can be distributed over a wide area and thereby facilitate the centralization of instantaneous communication makes it possible for the production plant to be removed from the seat of management the internal combustion engine has extended the network of transportation decentralisation has advantages to industry by reducing overhead costs and increasing efficiency to the individual it makes possible a better integrated family social and civic life possibly the greatest advantages and more healthful living especially for children the idea of city planning is of recent origin here is the center of one of many of our older cities which grew without much planning parks are shown in white the capital city was laid out on a plan of circles with radio avenues this architectural type of plan was quite satisfactory at the time here is a city laid out on the gridiron plan this plan was typical of all new american cities during the nineteenth century the motor age has necessitated a new approach in planning to direct automobile traffic away from parks residential areas and community centers this residential community  hazards of automobile traffic in pursuing the active life of home school and recreation most of our cities have grown without this modern type of plan for making them better places in which to achieve these new goals much of the old must be demolished substandard housing is giving way to decent homes the new type of housing gives fresh air and sunlight to all new park construction is needed to relieve crowded residential sections playgrounds take young and old off the street in safe and helpful recreation to relieve traffic congestion new arteries are cut through the city's at great expense the modern city is beginning to reflect the needs of the motor and mechanical age more and more cities will be planned as places to live with the greatest degree of safety efficiency health and happiness for all