This map depicts the United Baltic Duchy, a state which was proposed but never truly saw the light of day. Its creation was proposed by the Baltic German and Russian aristocracy towards the end of the Great War, and it was to be in personal union with the Crown of Prussia. The Kaiser declined the proposal historically for a variety of reasons, greatest of which was probably the fact that Germany wasn't exactly doing all that well in 1918, with the Allies gaining ground and the German Revolution making a mess of things at home.
In any case, in this universe - which I may or may not chose to develop further depending on how well this map is received - things went well for the German Empire in the Great War, and the Kaiser was in a position to accept the proposal from the Baltic nobles. This resulted in the creation of the planned United Baltic Duchy, with Adolf Friedrich, Duke of Mecklenburg, as the first head of state. (Under the Kaiser, of course.)
The divisions are based on what Wikipedia tells me is how they were going to organize this new United Duchy, with 7 cantons/districts total. Those seven cantons were to be Courland (and Semigallia), Latgallia, South Livonia, North Livonia, Estonia, Ösel and Riga.
Latgallia is all wrong. The reason for this is that the United Baltic Duchy on your map is made up of the 3 Baltic Provinces (Estonia, Livonia and Courland). The first 2 were annexed by Russia by the Treaty of Nystad (1721, from Sweden) and the last one by the 3rd Polish Partition (1795, from Polish suzerainty). But Latgallia, to the northeast of Courland, was annexed by the First Polish Partition (1772, from Poland) and, apparently being judged too small to form its own province, was joined administratively to territory to its east also annexed from Poland, eventually ending up as part of Vitebsk Province. So unless the people behind the United Baltic Duchy decided to apply the name incorrectly - and there's nothing on Wikipedia about that - or Wikipedia is wrong on there being a canton by that name - which, of course, you wouldn't find out from them - you need to modify the map. My guess is that you based yours on this one:
It shows a Baltic entity of sorts made up of Estonia, Livonia and most of Courland, as well as sections of Pskov and Vitebsk Provinces, including a part of Latgallia. The map is from 1920, after the United Baltic Duchy had ceased to be a factor but before the political situation had settled. It's the only map I've ever seen to depict that boundary, and I assume it to be a line of actual control prior to the Polish-Latvian conquest of Daugavpils (Latgallia's most important city) in January of that year. It vaguely resembles the Latvian-Bolshevik frontline on this map:
[link]
It shows a Baltic entity of sorts made up of Estonia, Livonia and most of Courland, as well as sections of Pskov and Vitebsk Provinces, including a part of Latgallia. The map is from 1920, after the United Baltic Duchy had ceased to be a factor but before the political situation had settled. It's the only map I've ever seen to depict that boundary, and I assume it to be a line of actual control prior to the Polish-Latvian conquest of Daugavpils (Latgallia's most important city) in January of that year. It vaguely resembles the Latvian-Bolshevik frontline on this map:
[link]
Anyway, here's a map of Latgallia in Latvia for reference:
[link]