The phrase N1 は(speaking of N1...) indicates the topic of the sentence, and the phrase N2 が represents the sub-topic, which is a part of N1.
この まちは せまい みちが 多いです。
Speaking of this town, there are many narrow streets./This town has a lot of narrow streets.
"Many people" is NOT 多い人, and "(a) few people" is NOT 少ない人.