二、The externality of urbanization research perspective

Urban agglomeration economy in essence. Agglomeration economy in three levels: first level is the enterprise internal agglomeration economy, its formation is the enterprise internal economies of scale; The second level are internal and external, industrial agglomeration economy, also known as the "regional economy", mainly through the industry function relation of externality and form; Third level is a multiple industry (industry) to the city of geographic concentration of agglomeration economy, also known as the "urbanization", formed the main reason is the industry of externalities. Urban economics emphasizes that industry in a city scale and spatial distribution of equilibrium is positive externalities and the negative externality of the same time. Urbanization is agglomeration economy in a country or a region of dynamic development process, when the process reaches certain standards, realize the urbanization. Cities provide rich is the essential attribute of external economies of scale.Economic geography that city is a kind of agglomeration economy, agglomeration economy is a kind of external economies of scale within the industry cluster, in due to the highly specialized pision of labor and cooperation within the cluster enterprises, enabling enterprises to share professional information spillover, specialized in the suppliers, specialization of labor market and so on. Enterprises of different industries in addition to share to private products production from industry as well as economies of scale of industry also share in the whole city for public goods and quasi-public products.Performance of the urban economy of scale. The enterprise in order to reach a certain threshold of the size of the market, over the minimum critical condition, the pursuit of economies of scale, tend to be in the city layout; Good investment environment and city development provides a good condition for the enterprise. In this way, enterprise and form the good pattern of the mutual promotion between the two cities. Enterprises to promote the process of the pursuit of economies of scale the expansion of cities, promote the development of the urbanization; The continuous development of city and improvement of for the enterprise development to create a more optimal.The development of the environment, more conducive to the realization of economies of scale, and attract more enterprises to this layout. The existence of external economies of scale, to the enterprise cluster have a huge gravity; Enterprises "cluster" and cooperation and pision of labor, production factors such as population agglomeration, support for the birth of urban industry and population, the factors of production, to promote the birth of the city, and also promoted the urbanization process.Today, on the other hand, due to the highly developed social pision of labor, market risk and uncertainty in the growing, inpidual enterprises, especially small and medium-sized enterprises (smes) cannot be effectively obtain internal economies of scope; On the other hand, the development of science and technology and the spread of globalization for the production system of vertical, horizontal pision of labor, a single enterprise production specialization, multiple enterprise collaboration, the formation of local production system, from each other in the cluster reveals the external economies of scope. As you can see, the role of monetary externalities are the main external economies of scope, is the enterprise in industrial cluster, enterprise (vertical direction) with customers, suppliers, subcontractors (horizontal) formed in the process of production through the market, thereby gaining the external economies of scope. External economies of scope is the disadvantages of small and medium-sized enterprises in the face of the market risk of the market response, "cluster" in a certain area for small and medium enterprises can provide huge economic attraction, undertake in the process of urbanization to absorb the rural transfer of factors of production (mainly) the most small and medium-sized enterprises in the cluster to enjoy external economies of scope, which can be set in the face of the market risk and all the force of the enterprise. External economies of scope, therefore, also have a positive role in promoting the city.Externality also promote urbanization by industrial cluster. In the process of urbanization, the city's role, from the viewpoint of economic geography is factors of production, industrial space geographic carrier. And the factors of production and industry is the space geographic concentration in cities, the main reason is that factors of production, the industrial concentration will produce agglomeration economy, agglomeration economy will reduce the production cost, improve production efficiency, also have gathered. The interest is one of the source of the externalities. The technical externalities by industry or other related industry enterprise of technology spillover and dry while learning new technology, new knowledge, new management, new technology, so as to bring its production efficiency and reduced production cost, make the enterprise obtain the benefits of externality. Currency externality is used to make the enterprise from the industry and relevant industry enterprises gathered in specialization of labor market, intermediate inputs, and professional services, etc., these make the enterprise production efficiency and cost reduction, make enterprise cluster enterprise income less than the outside economic interests, namely the economic benefits of currency externality. It is to get the benefits of these technical externalities and monetary externalities, on the one hand, enterprises tend to focus on space geographic, the focus is a dynamic, ongoing process, it attract industry and related industries as well as the service sector to join, rejection is not related industry to enter; Elements, on the other hand, there is also a tendency in the geographic territories, in addition to the pursuit of economic interests of the external, but also because of aggregation of related enterprise production.