By general agreement and city ordinance, all buildings must be faced with Jerusalem limestone, giving the city's different worlds an architectural unity and tying the city in a special way to the land on which it rests.
The city has a distinct appearance because of an architectural uniqueness in that all of their buildings' must use Jerusalem limestone for their facade. 
mnli hypothesis: The city has a distinct appearance because of an architectural uniqueness in that all of their buildings' must use Jerusalem limestone for their facade.  premise: By general agreement and city ordinance, all buildings must be faced with Jerusalem limestone, giving the city's different worlds an architectural unity and tying the city in a special way to the land on which it rests.