The history of the administrative divisions of the Imperial China is quite complex. Across history, what is called 'China' has taken many shapes, and many political organizations. For various reasons, both the borders and names of political divisions have changed—sometimes to follow topography, sometimes to weaken former states by dividing them, and sometimes to realize a philosophical or historical ideal. For recent times, the number of recorded tiny changes is quite large; by contrast, the lack of clear, trustworthy data for ancient times forces historians and geographers to draw approximate borders for respective divisions. But thanks to imperial records and geographic descriptions, political divisions may often be redrawn with some precision. Natural changes, such as changes in a river's course (known for the Huang He, but also occurring for others), or loss of data, still make this issue difficult for ancient times.