There aren't many mountains or hills in the town I live in, it's mostly flat.
ーThere aren't many mountains or hills in the town I live in, it's mostly flat, so most people ride their bicycles around town.
「私の棲んでいる町には山や坂があまりなくて平坦なので、街中では多くの人が自転車に乗っています」
There aren't many mountains or hills, it's mostly flat. で「平地で山や坂が少ないです」ことを表現できます。
in the town I live in で「私の住む町には」
to ride one's bicycles で「自転車に乗る」
ご参考まで!