Learn German: Die Fußgängerzone ist größer und nicht so eng. - The pedestrian zone is larger and not as narrow.

Many short, common German adjectives that contain an a, o, or u get an umlaut in their comparative (bigger/more) form. So groß (big) becomes größer (bigger/larger), just like alt (old) becomes älter (older).

How do you break down the long word Fußgängerzone?

Like many German words, it is a compound built from smaller pieces: der Fuß (the foot), der Gänger (walker/pedestrian—from the verb gehen), and die Zone (the zone). The gender of a compound noun always comes from its final word, which is why the whole word uses the feminine article die.

Since this lesson is about the accusative preposition durch (through), why is die Fußgängerzone in the nominative case here?

This sentence is simply describing the zone, not talking about moving through it. Because the zone is the subject of the sentence (it is the thing doing the "being"), it stays in the nominative case. If you wanted to say "I am walking through the pedestrian zone," you would use your lesson's grammar: Ich gehe durch die Fußgängerzone. (Luckily, feminine nouns use die for both nominative and accusative, so it looks the exact same anyway!)

The English translation says "not as narrow", but the German uses nicht so eng. Are so and "as" the same here?