Conversation so far:
What was Frederick Law Olmsted's involvement with central park?
Frederick Law Olmsted and Vaux entered the Central Park design competition together.
Did Frederick Law Olmstead and Calvert Vaux win the central park design competition?
Frederick Law Olmstead's and Calvert Vaux's Greensward Plan was announced in 1858 as the winning design.

Question: what was special about their design?
Self-contained rewrite: What was special about Olmsted and Vaux's design for Central Park?