In international law, there are three main ways to divide the boundaries between countries: 1, natural demarcation method; It refers to the division between countries by using natural terrain such as rivers (with the center line of the main channel as the boundary), lakes (with the center of the lake as the boundary), mountains and rivers (with the watershed as the boundary) and rivers without waterways (with the middle of bridges on the river as the boundary). 2. Geometric demarcation method; It refers to dividing national boundaries with a straight line between two fixed points! 3. Astronomical delimitation method; It is a method to determine national boundaries with a certain latitude and longitude!