Britain is not the size of South America, but Westeros really is that big. Westeros does not map directly onto the real world because it’s fantasy. I would caution against exact real world / historical parallels when it comes to ASOIAF. There are parallels to be made; for example, the War of the Five Kings has a lot in common with Shakespeare’s telling of the War of the Roses. However, a fan reported that GRRM said:
if [you] looked hard enough [you] could see many similarities to other historical figures - such as Henry VIII in Robert, and Richard III in Tyrion. […] Some fans have taken that too far and have looked for exact parallels to the Wars of the Roses, to say this character is actually Edward IV and this character is Richard III but none of that really holds up. My characters, while they may be inspired in one facet or another, are not actual historical characters under other names. I prefer to do something other than that.
A similar concept applies to the world building and geography. GRRM has said:
Over the years, more than one reviewer has described my fantasy series, A Song of Ice and Fire, as historical fiction about history that never happened, flavored with a dash of sorcery and spiced with dragons. I take that as a compliment. I have always regarded historical fiction and fantasy as sisters under the skin, two genres separated at birth.
In ASOIAF, GRRM has written descriptors like "brown as a Dornishman" to indicate that the Martells are not white people. GRRM told Janina Gavankar, an actress of Indian ancestry, that she “look[ed] like Lady Nymeria" Sand.
Please read this post I am linking here.
Many people consider Dorne to parallel Asia / Africa, because a lot of the official artwork approved by GRRM closely resembles real world places and architecture (please click all the links in that post). There are no barren, hot, sandy deserts in Europe where people die from lack of water; there are such things in Dorne. During the Conquest, sandstorms engulfed entire companies of Aegon’s soldiers, and they ~vanished into the sands~. There are deserts in India. When the “orphans of the Greenblood” spoke of the “Mother Rhoynar,” I immediately associated it with the Ganges River in India and its “mother” aspect.
You might try looking in this tag or this tag on asoiafuniversity. You might also try asking fatpinkcast because the people running that blog are much more knowledgable about this issue than I am.
I will not be discussing this topic further.