I was looking at the memory map of the GBA (as in page two of
http://www.ziegler.desaign.de/GBA/gameboy_advance_for_nongaming_applications.pdf\
)
and I guess I don't understand the convention. For instance:

External 0x02000000 256 KB 16 bits

Internal 0x03000000 32 KB 32 bits

IO Ram 0x04000000 1 KB 32 bits

Why does there seem to be equal distances between unequal sizes of
memory? Are the addresses just arbitrary labels? Or do they refer to
actual locations in the physical memory?