Not only the Germans but all human populations have been and are interested in this question: Do we have enough - do we need more Lebensraum? This page collects some data on the question whether China's living space is enough or not.
Can China feed itself? This question was the research focus of a Prof. Heilig at the International Institute for Applied Systems Analysis in 1999. The interactive work combines insights from agricultural, geographic, demographic and many other disciplines.
Chinese geography. Here is a good selection of maps on Chinese geography compiled by Columbia University. It is worth a remark that the link to historical boundary maps is blocked in China. Below is a simplified overview that shows that the territory of China has expanded and shrunk over the last 2500 years like that of most other countries / civilizations that have such a long history. Wikipedia has a great animated version that will be dismissed by all Chinese nationalist.