Oops, meant to say "there are 20 TILEs across the screen top", not ten. It helps also, to imagine each 'stamp' as in a regular text character sized box.
For those interested in game development / production tools (MK14 et Al) I used the HESMON debug monitor, a game cartridge with ROM that could take over, for examine 6502 (6510) registers in usual bug fighting.
But that was the limit of (my) expertise. Bought my system, thick Commodore users manual, dot mat printer, (and HESMON cart) at TOYS 'R US... Yeah, I know, pretty saavy, there.
Ted (also Larry) was the real hero... Supplied support with MS-DOS system, for the glue that brought all together, graphics, code, disk loader; All that came Via MSDOS... saved all our butts.
The artist had a MAC, the only real system in that office! It was shared, president, marketing, shipping, everyone used that one 1985 Apple Mac.
Things didn't go well, always, and I don't say that to complain: My choice here is to avoid the colorfully history, for helping those wanting to write CODE, on a C-64 orig or heritage copy. Hayward city is 30 minute drive, to former ATARI buildings, by the way. I could write, colorfully stories, "lookit those older bullet holes, in my apartment wall, there". But for that, remember that movie: 'Pulp Fiction'. (Hayward has similar past).
Looking at first diagram, shows 4 of the bit-map 'stamps' making up one TILE. A register-indirect creates each for color. Your bit pair will specify the register, that's in one of 3 places, each a byte, in coordinated blocks, elsewhere in RAM. So a 11 for example, tells hardware (video VID IC) to use the color RAM, to get the ultimate color.
For two other colors, the indirect points to proper nibble (register) this time in the 1k 'screen RAM'; that's where text typing is, in low res modes.
So you've got maps all over the place, different resolutions, result is you can call 'FourColor', chosen from 16 possible color options. One subtle aspect, using the common TILE and STAMP system, the stamp provides shape, the tile assigns colors, so a full screen can include ALL shades, the restriction comes at each little local area, with four (shades) available.
Clear as mud, plus my babbling. Don't let that quit you:. Get the damn BOOK!
Now, the first diagram was limited, to show a single color (actually that's a sprite, SPACE-SHIP), and second diagram shows full TILE: the green pixels are done register-indirect, to using high nibble, corresponding directly to that mapped stamp. Literally,
the full 8k is mapped down into corresponding 1k, which is calculated using quick bit shifting, but also zig-zagging along with the hi-res zig-zagging map..
WHEW, this is hard to explain, consider!
Clearasmud, clearasmud.
Now, take a glance at the hex address, see the left side, of a TILE at 4100 h. Notice the lower stamp; it has location 41A0 h. That shows, right there, the 160 byte offset, A0 h being 160 decimal. To follow that, you walk down, 8 bytes(lines) then zigzag up to next stamp. Doing that across gives 160 bytes, 40 stamps by 8 bytes each. OR, 20 TILES across, remember each is a 2 by 2 organization.
For those truly into doing some, please look around for that (thick) Commodore book / manual... It was 6 by 8 inches, with heavy binding loops.
That maybe clear but not at first!