Is Finland a part of Scandinavia? (Basically, is Scandinavia determined by geography or culture)?
Strictly speaking, "Scandinavia" is comprised of Sweden, Norway, and Denmark. The "Nordic" states would be those three plus Finland and Iceland.
Finland, especially western Finland, historically has been heavily influenced by Sweden, many ethnic Swedes live there, and Swedish is spoken widely--again, especially in western Finland.
Ethnically and linguistically, the Finnish people and language are quite distinct from the Scandinavian peoples and languages.