When you talk about geographic borders of dialects, you talk about isoglosses.
What is an isogloss?
An isogloss is a geographic boundary between two linguistic features. One famous example of such an isogloss in Germany is the Speyer line. The German word »Apfel« (English: apple) is pronounced [ˈap͡fl̩] (like »apfl«) in Standard German and in dialects spoken south of this line, but in the dialects spoken north of this line people pronounce it as [ˈapl̩] (like »appl«), and so this line is also called the »Appel-Apfel-Linie«
The Benrath line
More important is another isogloss, the so called Benrath line that roughly goes from Aachen in the west to Frankfurt/Oder in the east. The exact course is described in the German Wikipedia article about the Benrather Linie.
In fact it’s not a single line, but a bunch of many closely located lines separating different linguistic features. One of them is the »maken-machen-Linie«: The German word »machen« (Engl: to make) is pronounced [ˈmaxn̩] in Standard German and in Dialects south of this line, but north of this line people say [ˈmakn̩]. And geographic almost (but not perfect) identic are other isoglosses: The »ik-ich-Linie«, the »dat-das-Linie«, the »Dorp-Dorf-Linie«, the »hebben-haben-Linie« and many others. These isoglosses are geographic so similar, and there are so many of them, that they were given a common name, and this is Benrath line. It is a rather sharp line, and all isoglosses that belong to it are only a few kilometers apart from each other.
Niederdeutsch, Plattdeutsch (Low German, Low Saxon)
Dialects spoken north of the Benrath line are called Niederdeutsch or Plattdeutsch. In English you also have two names for it: Low German and Low Saxon. The name comes from the low and flat land where it is spoken.
There are Wikipedia articles available for it
When you try to read the article about Low German in Low German, you will find, that it is very different from Standard German, and for this reason most linguists define Low German as a distinct language. But since it is spoken in an area where also Standard German is taught in schools and where all official documents are written in Standard German, almost every native speaker of Low German is bilingual and also speaks Standard German (although sometimes with a heavey Low German accent). And for the same reason there are dialects spoken in this region that are a mixture of Low German and Standard German.
I should also mention, that Low German is also spoken in the eastern regions of the Netherlands and that there are isoglosses running through the Low German region that separate it in smaller regions where different variations of Low German are spoken. And I should mention, that Niederdeutsch, Plattdeutsch and Niedersächsisch are not 100% identic to each other. There exist three different definitions for these three variations, but I’m not going to spread that out here. If your’re interested in this topic, you can read the Wikipedia articles.
Hochdeutsch (High German)
When you move southwards through Germany, the sea level increases more and more, until you reach the alps in the south. And because the land south of the Benrath line is higher, the language spoken south of this line is called »Hochdeutsch«. But be very careful with this term, since it has two different meanings:
- Hochdeutsch (High German) is a group of German dialects. It is not taught in schools, not used for official documents, and not used to print books and papers.
- Hochdeutsch (Standard German) is a standardized cross-regional language taught in schools, used for official documents (like laws etc.), and used to print books and papers.
Here in this answer I consequently will use the term »Hochdeutsch« as defined in item 1, while I will use the term »Standarddeutsch« for what is described in item 2. The English terms »High German« and »Standard German« are much clearer.
There are Wikipedia articles available for it
Note, that the English article talks about High German languages while the German article describes them as dialects. This is because linguists have divergent opinions of what the difference between a language and a dialect might be.
But this questions topic is about the geographic properties of German dialects, so I keep with the term »dialect« and have a closer look at geographic properties, and here the Speyer line from paragraph 1 comes in handy, because it separates the High German region in two parts: »Mitteldeutsch« and »Oberdeutsch«.
Mitteldeutsch (Central German)
Central German is the name for the group of dialects spoken between the Benrath line and the Speyer line. They are also spoken outside of Germany, in Luxemburg and parts of Belgium. And for this reason, German (Standard German to be clear) is also an official language in these two countries.
Also Central German can be subdivided by several isoglosses into smaller regions where sub-dialects of Central German are spoken, which differ strongly when you move from east (Dresden) to west (Köln = Cologne). For more details, please consult Wikipedia.
Oberdeutsch (Upper German)
The dialects south of Speyer line are called »Upper German«. You can find it in Wikipedia:
You clearly can differentiate it from Central German and even more from Low German, but Upper German is so diverse and spread over such a big area, that it is divided in four languages or dialect groups, where one of them has become extinct 1000 years ago:
- Ost- und Südfränkisch (East and South Franconian)
- Alemannisch (Alemannic German)
- Bairisch (Bavarian)
- † Langobardisch (Lombardic)
Lombardic was spoken by the Lombards in northern regions of Italy, but it was spoken only between about 600 AD and 1000 AD. But the other three still living languages are worth a closer look:
Ost- und Südfränkisch (East and South Franconian)
East Franconian is spoken for example in Nürnberg and Würzburg, South Franconian in Karlsruhe.
East Franconian has some properties in common with Central German, but still most linguists put it in the group of Upper German dialects. South Franconian more clearly belongs to Upper German.
Links to Wikipedia
in Standard German
Alemannisch (Alemannic German)
This group of dialects is spoken in many countries like France (in Alsace and the Canton of Phalsbourg), Liechtenstein (in the whole country) and Austria (in the state Vorarlberg), but the main regions are
- in Germany in South Baden (Südbaden, state of Baden-Württemberg) and Swabia (Schwaben, states of Baden-Württemberg and Bavaria)
- all German-speaking regions of Switzerland
There are Wikipedia articles about Alemannic German available
The status of Alemannic German in Germany is relatively clearly that of a group of dialects that are used in unofficial settings, like among friends or inside a family. But in Switzerland is has the status of a distinct language used parallel to the Standard German language.
In Switzerland Standard German language is almost only used for writing, but not to speak. When Swiss people speak, they use the Swiss variation of Alemannic German which they call »Schwyzerdütsch« (Swiss German). Radio and TV shows produced in Switzerland for Swiss people are produced in Swiss German which is unintelligible for most people outside of Switzerland.
Swiss German was used for writing among many centuries only in very rare cases and so it is not standardized (there are no official rules for orthography). But since Swiss people use SMS and boards on the internet, they about 20 years ago began to write no longer in Standard German but in Swiss German. And for this reason, Swiss German has of all languages and dialects discussed here the highest chances to survive also for the next 100 years, while all other versions of German slowly will become extinct in this century (as I believe) and will be replaced by Standard German.
Swiss German in Wikipedia:
This is the kind of German spoken in large areas of Bavaria (Altbayern), small parts in the west of Saxony, almost all of Austria (all states but Vorarlberg) and South Tyrol which is a region in the north of Italy (next to North Tyrol and East Tyrol which both belong to Austria).
Also Bavarian differs strongly from Standard German, so that it is unintelligible for many German native speakers living in northern regions. And so many linguists classify it not as a group of dialects, but as a distinct language.
And since it has so many speakers and is spread over a large geographic area, it also can be subdivided by isoglosses into regions with subvariations:
- Nordbairisch (North Bavarian), spoken only in Bavaria
- Mittel- or Donaubairisch (Middle or Danube Bavarian), spoken in Bavaria and Austria
- Südbairisch (South Bavarian) spoken only in small parts of Bavaria but large regions of Austria and in Italy.
Bavarian in Wikipedia:
Standarddeutsch (Standard German)
I mentioned Standard German many times in my answer, so I think I should tell something about it too:
You very often will hear the term »Hochdeutsch« for Standard German, but this term is ambiguous, as explained earlier in this answer. Mainly in Switzerland you also will find the word »Schriftdeutsch« (written German) used for Standard German, because in Switzerland Standard German is very rarely used for speaking, mainly only for writing.
Standard German is what you learn when you learn German as a foreign language, but you should know, that it in some manner is an artificial language, because, as you will know, when you have read this answer so far, German is not one language. Over probably more than 15 centuries many different West-Germanic languages like Bavarian, Saxonian, Franconian, Alemannic, Lombardic etc. were spoken in the region where now is spoken the German language. And the modern German language developed from this mixture of different languages, and many attempts have been made to create a language that everybody could understand who lived in this region.
Among many attempts maybe Martin Luther’s translation of the Holy Bible into German was one of the biggest steps to create something like a standardized German.
This process has not come to an end yet. It is still going on, and it will only end in one German, when every German native speaker no longer speaks their local or regional dialect, but only standard German. This is the day when all languages discussed here will have become extinct.
German standard variations
But now even the standard exists in three different flavours, the three standard variations of German. This is a layer above the layer of dialects, ignoring isoglosses that separate the historic grown borders between dialects. The borders of the three standard variations are political borders between nations.
- German Standard German
used in Germany, Belgium and Luxemburg
Wikipedia: English; German
- Austrian Standard German
used in Austria and Italy (South Tyrol)
Wikipedia: English; German
- Swiss Standard German
used in Switzerland and Liechtenstein
Wikipedia: English; German
So, what does used mean in this context? It means that laws and other official documents are written in these variations, and it means, that these variations are taught in schools. Also regional newspapers are printed in these variations, and politicians and news speakers use these variations.
But books are (except some rare exceptions) only printed in German Standard German. This is, because about 85% of all German native speakers live in Germany, and German people don’t know Austrian or Swiss Standard German. But every German native speaker in Austria and Switzerland knows German Standard German and can understand it.