The whole field is a 16×16 grid of /8 blocks ordered by the first octet (column = low nibble, row = high nibble ×16; octet = row + column, written inside each block). The labels above and to the left of the map are the column and row numbering.
This mode:
inside a /8 the same rule nests — /16 by the 2nd octet (16×16 tiles), /24 by the 3rd octet.
IPv4 Address-Space Map
1 cell = one /24 · 4096×4096 = whole 2²⁴ space · grid of 16×16 /8 blocks by first octet.
How to read the map (legend)
announced (BGP)
unannounced (allocated, dark)
technical / reserved
unallocated
0123456789101112131415
0163248648096112128144160176192208224240
Top = column (low nibble) · left = row × 16 (high nibble) · first octet = row + column; the number inside each block is that octet.