What is a Map?
A Map is an Array, which having the addresses of the free space in the swap device that are allocatable resources, and the number of the resource units available there.
Address Units
1 10,000
This permits First-Fit allocation of contiguous blocks of a resource. Initially the Map having one entry - address (block offset from the starting of the swap area) and the total number of resources.
Kernel treats every unit of Map as a group of disk blocks. On the allocation and freeing of the resources Kernel updates the Map for accurate information.