Masjumi and the smaller Muslim parties Perti and PSII dominated the elections in Sumatra. The PKI's following was strongest amongst Javanese settler communities in North and South Sumatra. Map shows parties winning 5% or more of the vote, by province.
Feith, Herbert, The decline of constitutional democracy in Indonesia. Ithaca NY: Cornell University Press, 1962.
Herbert Feith, The Indonesian elections of 1955. Ithaca, NY: Cornell University Modern Indonesia Project, 1957.