请教用where还是which:conveyance of emigrants had developed to the

请教用where还是which:conveyance of emigrants had developed to the point where larger
conveyance of emigrants had developed to the point ((where)) larger profits were being made by the "passenger trade" than by the carriage of timber of European goods.
((where)) 难道不用which吗?指代前面的point（程度）.为什么用where?