A fascinating book regarding the demographics of late Ottoman era Macedonia is "Maps and Politics: A Review of the Ethnographic Cartography of Macedonia" by Henry Robert Wilkinson. In his book, which was published in 1951, Wilkinson exhaustively summarized dozens of ethnographic maps put forth by European scholars, ethnographers and cartographers which depicted the demographics of the southern Balkans.
From the dozens of ethnographic maps included in Wilkinson's book it is appearent that up until the late 19th century the Slavs of Macedonia were regarded as Bulgarians. The following is how Wilkinson described the process in which the Slavs of Macedonia came to be regarded as an ethno/political group distinct from the Bulgarians in the region. Wilkinson's position surely does not concur with the mythical historiography being promoted by nationalists from the Former Yugoslav Republic of Macedonia (F.Y.R.O.M) which asserts that 'ethnic Macedonians' have continuously resided in the region since antiquity.
Wilkinson's exhaustive study and detailed analysis of the ethnographic studies pertaining to Ottoman era Macedonia resulted in his assertion that no authority depicted the Slavs of Macedonia as an ethnic group distinct from the Bulgarians until certain European ethnographers and cartographers were influenced by the politically motivated works of the Serbian scholar J. Cvijic who espoused the contemporary Serbian policy of diminishing Bulgaria's claim to the region. If "ethnic Macedonians" dominated the demographics of the region for dozen(s) of centuries, as nationalists from F.Y.R.O.M constantly claim, why did dozens of pre 20th century studies and publications pertaining to the ethnography of the region fail to record what was supposed to be obvious: a significant 'ethnic Macedonian' population? Of course, the answer to this question is obvious to any objective historian: the "Macedonian" ethno-national identity was a late 19th century construct and no significant population affiliated with the "Macedonian" identity until the 20th century. The dozens of ethnographic maps depicted in Wilkinson's book also destroy the theory currently being promoted on many F.Y.R.O.M nationalists websites (see maknews.com) which asserts that no Greeks existed in the pre 1912 region of Macedonia.
These are a few examples of the ethnographic maps found in Wilkinson's book. The demographics depicted in the maps may differ from one another but what is important to note is that no "ethnic Macedonian" population was recorded.
Nationalists from F.Y.R.OM attempt to explain away these vast number of maps and surveys (including the 1914 Carnegie Report) by claiming that the authors were ignorant of the truth, and/or blinded by bias, and/or uneducated. This would be akin to a vast number of studies being published pertaining to modern Palestine and not mentioning any Palestinians!