20% is 1/5. It is still too much but not the end. 80% did not vote for them. And the left go stronger too and keeps growing. This is the beginn of the fight, not the end.
“Extremes” both sides, ie. the Nazis and the Left party, are more popular in the east, no doubt because it is poorer, so people are less satisfied with the status quo.
It looks like it's just West-Berlin + a suburb of West-Berlin, while the rest of old East-Germany went fascist.
Edit: I had misread the map when I made the above comment. The CDU in West-Berlin are not the only non fascists, East-Berlin has not gone fascist, but mostly went for Die Linke.
Sorry, I apparently had misread the map, I thought east-berlin had mostly gone afd as well. The color of Die Linke had blended in with the color of afd, so it had seemed like it was just an island of black colored west-berlin in a sea of afd.
And yes, I'm partially color blind, which isn't an excuse, but might explain it a little.