Country's borders, also known as national boundaries. The territory of a country's geographical boundaries with its neighbors. Boundary line is within the territory of a country is sacred and inviolable. On the map, the boundary line is a line winding, but is not the case in the field. A country's territory is a sovereign country under the jurisdiction of all the territory, including land, waters and its subsoil and over. So, the country's border is the boundary line from the surface as the base for vertical upward and downward posed like an invisible wall. Therefore, the border is a closed vertical surface dry surface, rather than a line on this for a very high to very high sky, deep deep down into the earth's crust.
         The formation of the border is also a long historical process. Ancient society, as a result of restrictions on scientific and technological level, inter-country competition in the territory of the main surface, and at the end of the air and soil has yet to learn, then it is just a line boundary. With the development of the aviation industry, followed by airspace sovereignty. With the rapid development of industries, industrial production resources required by the growing importance for all countries, and industrial resources required for the majority of reserves in the subsoil, some still in the sea, in the development of the process of soil on the soil at the end there was the issue of sovereignty . Therefore, airspace and land at the end of the problem, the international community made a number of corresponding measures of protection and the form of international law. Such as aircraft and ships, in particular military aircraft and warships can not enter another country's airspace and territorial waters, the submarine under water can not enter the territorial waters of other countries and, of course, can not be within the territorial waters of other countries to develop undersea oil and mineral deposits, such as mining. In this way, the border has become a natural extension of the vertical upward of downward.