What does the whole base58Prefixes[PUBKEY_ADDRESS] in code reference?

[number435398]

Example:
base58Prefixes[PUBKEY_ADDRESS] = std::vector<unsigned char>(1,48);

I know the last part, the "48" in this case, references an "L" as being the first character of an address.

What does the 1 reference?  What are some examples of changing it and what will changing it do?