Unexpected Smell-Based Navigation System - (Speaking > Unusual Situation)

You are visiting a new city and discover that the entire navigation system is based on smells instead of visual cues or maps.

Call a friend who is planning to visit the same city next week.
Describe this unusual navigation system in detail and explain how it works.
Give your opinion on whether this system is effective or not, and provide recommendations for your friend on how to prepare for and use this unique navigation method.