Variable designations

Blocks of variable numbers are allocated as follows:

	a01-a99   Unit-control variables
	a101-a999   Raw-data variables
	a1001-a9999   Regional-analysis variables
	a10001-a10999   Analytical variables

The need for 5-digit numbers stems from the advantage of reserving 4-digit numbers for the regional-analysis variables. There are nine macroregional systems, numbered R1 (Manchuria) to R9 (Yungui), many of which have subsystems, and the same variables are created for each macroregion and subregion separately. It is much easier to keep things straight when the initial two digits in a 4-digit ID always indicate the regional system in question; so a5004 is the core-periphery zoning of the Middle Yangzi treated as a whole, while a5104, 5204, 5304, and 5404 are the core-periphery zonings of its component subsystems, respectively. The contrast between 3-digit IDs for raw data and 5-digit IDs for analytical variables serves to distinguish the two kinds of variables and permits parallel substantive assignments. So, for instance, a10201-a10299 would be the analytical variables derived from a201-a299.