there are ---more people in our city than in yours 中---是填muc

注意：这儿有一个有介词than引导的比较状语than in yours （比在你的城市里）,因此前面的形容词要用比较级,more就是比较级.修饰比较级的程度副词主要有：slightly,rather,a bit,much,even,still,far,alot,a little,a great deal 等；
many more修饰可数名词复数,much more修饰不可数名词.
另：英汉大词典（陆谷孙）435页,deal 2 .2)大量,极大限度：We were a deal happier than their children.我们比他们的孩子要幸福的多.
所以答案是：a great deal