Q: Why was the entire map covered by a buffer with the radius of 5?
A: The wrong buffer radius you input might cause this error. This problem mainly occurs in datasources with latitude and longitude coordinate system. Since the unit of the buffer radius is consistent with the unit of the dataset, if you are using a datasource of a latitude and longitude coordinate system, the radius is in degrees. Therefore, the number 5 you input indicates 5 degrees, not 5 meters as you expected. The solution for this problem is to convert the radius of the buffer into a value in degrees. For example, to create a 5 meters wide radius buffer, you need to convert 5 meters to 0.00004 degrees, and then input the buffer radius 0.00004 in the dialog box to generate the buffer correctly. (1 second approximately equals to 33 meters).
