Complex sentence: The address is fictitious, being slightly higher than the highest Vanderbilt Avenue address, but were it to exist it would be within Prospect Heights' boundaries, as Vanderbilt Avenue ends at Grand Army Plaza.
Split into simpler sentences: The address is fictitious, being slightly higher than the highest Vanderbilt Avenue address. Were it to exist it would be within Prospect Heights' boundaries, as Vanderbilt Avenue ends at Grand Army Plaza.