Ethnolinguistic map of the Russian Empire according to 1897 census.
Own work
Census data taken from demoscope.ru website:

The First General Census of the Russian Empire of 1897. Breakdown of population by mother tongue and districts* in 50 Governorates of the European Russia
Распределение населения по родному языку и уездам Российской Империи кроме губерний Европейской России
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