A synonym is a word that has the same meaning as another word even though their spellings may be different. They all denote the same meaning and thus, can be used as and when necessary.
In the given sentence, the word in italics is "erect". In general, 'erect' means straight. But in this case, the word is used to mean that the city plans to construct, to build the new structure.
Thus, the synonym that has the same meaning as the word "erect" is "build".
