The Apple IIgs memory map is a bit convoluted because of its compatibility with the classic Apple ][ setup.
The lowest 128k are set up like in the IIc: (48k main memory + 16k "Language Card" memory) * 2. The language card memory is bank-switched with the Apple II ROMs, because when in 6502 mode, the IIgs can address no more than 64k without bank-switching ) and the IIGS needs to behave like an "old" Apple II.
The rest of the standard 256k is only accessible when the 65816 runs in its native, 16-bit mode. Any memory expansion that goes in simply linearly attaches to the 256k upwards.
The Apple II memory emulation is controlled by the "Mega II" chip that basically emulates a classic Apple II memory layout in the lowest 128k. This lower half of the IIGS standard memory is run at 1MHz, just like in the Apple II (so it's "slow" memory).
The upper half of the 256k is run outside the bank-switched area controlled by the Mega II at full speed of the 65816, so it's "fast memory" ran at 2.8MHz (and any memory you add using IIGS memory expansion cards is also "fast memory").
None of the marked PCB areas are actually ROM. To make thinks even more complicated, the IIGS also has "slow" (i.e. Apple ][-compatible) ROM and "fast" ROM only used in IIGS-native mode.
