The first member has an acute accent (udātta) on the first syllable before the word nagara but not when it is the word mahat or nava , nor when it refers to a city in the lands of the Northern People.,
Thus सु꣡ह्मनगरम्, पु꣡ण्ड्रनगरम्, वि꣡राटनगरम् ॥ But not in महानगरम् and नवनगरम्, Why do we say \but not of Northern People\? Observe नान्दीनगरम् कान्तीनगरम् ॥,