The FIDE system of zonal and interzonal tournaments was not yet firmly established and so most participants of the first interzonal, starting July 15th, were selected by FIDE ballot.
Hilversum Zonal 1947 gathered the champions of the various European FIDE member nations together. O'Kelly de Galway of Belgium came 1st, but must have declined to play at Saltsjöbaden. Trifunovic and Pachman shared second. Szabo came in a tie for fifth. Pirc, Gligoric and Tartakover were not invited to Hilversum, but were nominated by ballot by the FIDE directors to play in the Interzonal.
Böök and Stoltz were joint winners of the "Nordic" zonal, Helsinki 1947, in which Lundin ended 5th.
All Soviet players were selected based on their results in ballots submitted by the FIDE directors. Boleslavsky came second at the 15th USSR ch. 1947, and Bondarevsky shared 3rd.
Lajos Steiner was selected by FIDE ballot to represent Australia.
Isaac Kashdan came in second at the U.S. ch. of 1946. Reshevsky the winner was seeded into the 1948 World ch. at The Hague/Moscow, and Kashdan qualified to play at Saltsjöbaden IZ 1948. Arnold Denker was selected by FIDE ballot, but apparently both Kashdan and Denker declined to play. Israel Horowitz seems to have been offered a place as a replacement, but must have declined as well.
Najdorf and Stahlberg shared first and Erich Eliskases came third in a strong tournament at Mar Del Plata in 1947. Eliskases must have declined to play.
Yanofsky qualified as winner of the Canadian ch, Quebec 1947.
Crosstable of the interzonal: http://storiascacchi.altervista.org...
# 1-8 qualified for the candidates tournament, along with the 4 losers of the WC match tournament (Keres, Smyslov, Reshevsky, Euwe).