This is one of the most surprising map layers. Of the 59 sheets of the Piadyshev atlas, only one includes mosques in its legend. If you were to take the atlas as an authoritative source for the cultural geography of the empire, you would have no choice but to conclude that there were but four mosques in the entire Russian Empire, and that all of those mosques were located within 175 kilometers (roughly 100 miles) of each other, along the Akshi-kun and Nura rivers, both of which flow into Lake Kurgaldzhin in Omsk province. (Click here to see them on the interactive map.)
Why did the Military-Topographical Depot choose to include these mosque locations, and not the thousands of others dotting the landscape of the Volga provinces and Tavrida? A question worth mulling, to be sure.