what does "draw lines" mean here?

"And there are a number of things that we can always co-operate on, and the list is pretty public. But there are also areas of friction, be it Taiwan, or the South China Sea. And you suggest that we need to draw lines. Now, we can’t draw them everywhere, but the matter of the South China Sea does raise questions in terms of Indonesia, Malaysia, the Philippines, and other nations in the region." in this paragraph, what does the sentence"And you suggest that we need to draw lines. Now, we can’t draw them everywhere" mean?
Anyone can offer me help? Thanks a lot！