Roberts, Toby; Williams, Ian; Preston, John (2021). „The Southampton system: A new universal standard approach for port-city classification”. Maritime Policy & Management. 48 (4): 530—542. S2CID225502755. doi:10.1080/03088839.2020.1802785.
„Cities of Finland”. Eurostat. Архивирано из оригинала 18. 5. 2013. г. Приступљено 10. 2. 2013.CS1 одржавање: Формат датума (веза)
hel.fi
„International Relations”. Hel.fi. City of Helsinki. Архивирано из оригинала 26. 09. 2017. г. Приступљено 11. 6. 2017. „Helsinki’s main bilateral city partners are St. Petersburg, Tallinn, Stockholm and Berlin. In addition, Helsinki maintains special long-term partnerships with Beijing and Moscow. Helsinki has no official sister cities. Helsinki primarily works with other capitals.”
Roberts, Toby; Williams, Ian; Preston, John (2021). „The Southampton system: A new universal standard approach for port-city classification”. Maritime Policy & Management. 48 (4): 530—542. S2CID225502755. doi:10.1080/03088839.2020.1802785.
„Cities of Finland”. Eurostat. Архивирано из оригинала 18. 5. 2013. г. Приступљено 10. 2. 2013.CS1 одржавање: Формат датума (веза)
„International Relations”. Hel.fi. City of Helsinki. Архивирано из оригинала 26. 09. 2017. г. Приступљено 11. 6. 2017. „Helsinki’s main bilateral city partners are St. Petersburg, Tallinn, Stockholm and Berlin. In addition, Helsinki maintains special long-term partnerships with Beijing and Moscow. Helsinki has no official sister cities. Helsinki primarily works with other capitals.”