How were ethnographic maps in the 19th century made?

Question

Ethnographic maps are visual representations of the ethnic make up of particular regions. Usually multicultural regions which are controlled by an empire.

Here are some examples of ethnographic maps:

German map of Epirus in 1878

German map of Greece and the Balkans in 1876

German map of Greece and the Balkans in 1847

a lot more on this page

Looking through these various maps one notices that each one shows quite different picture to the others. I am aware that such maps often use different criteria to characterise people (eg language, religious affiliation, self identification, or other characteristics). I am also aware that probably all ethnographic maps are biased in some way or favour one particular political/national cause over another.

What I haven't been able to understand though is how data on these maps were actually gathered. Did cartographers go to every single village in a particular area to get their data? or did they visit one or two villages in an area then make a general conclusion about the rest?

I have been to Epirus and have seen how difficult it is to navigate to remote villages even to this day. I'm sure that the rest of the Balkans had villages which are just as hard to get to yet somehow we have ethnographic statistics on them in the mid to late 1800's and before modern highways. So how did cartographers go about creating these?

Answer 1

A detail that pops out looking at a couple of these maps is the cartogropher, Heinrich Kiepert. Instead of speaking in general terms about the maps, we can, at least partially, answer the question by looking at Kiepert. An article here discusses his credentials:

Kiepert was head of the Geographisches Institut in Weimar between 1845 and 1852 and professor at the University of Berlin from 1852.

So as suggested in comments, the cartographers are often members of academic organizations, which give them other resources to draw upon to aid them in their work. But they do field work as well (same source):

Another major interest was the Ottoman Empire, where Kiepert travelled numerous times, gathering enough data to produce several major maps of the Ottoman world between the 1840s and 1890s.

The wikipedia article also points out earlier travels in his youth. So we see some travel was definitely involved in the process. So a combination of field work and academic research are implied, with varying amounts of each depending on circumstance.

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For little more direct information about the ethnographic maps, and specifically those about the Balkans, an article(pdf) on Ethnic Mapping on the Balkans (1840–1925) addresses some of the sources used by Kiepert (pdf pg 15):

Kiepert‘s work was based on the data of Sax, Jireĉek, Kanitz, Bradaška, Jakšić and the map of Lejean and Hahn.

So we can see these maps drew at least some information from others data. (The paper has a lot of information about the difficulties ,inaccuracies and motivations concerning the ethnographic maps of this region.)