• Aligning the interests of everyone involved — city councils, residents, telecom firms, utilities, app developers — is often a political quagmire.
• And discussions are happening with the backdrop of increased skepticism of big tech companies — many of which are trying to sell tools to cities.

A foremost pain point is who controls the data generated by millions of sensors and cameras.

• "The last thing we want is a smart city of surveillance. Freedom goes out the door," says Ann Cavoukian, former information and privacy commissioner for Ontario, Canada, and a city privacy expert at Ryerson University.

Rising housing prices are another hurdle. Some of the largest and most expensive metro areas — such as New York, Seattle and Los Angeles — have been among the most hospitable to smart city discussions. But Americans are finding it harder to afford these areas in the first place.

• Mid-sized cities — such as Columbus, Kansas City and Phoenix — are harnessing smart city projects to attract attract workers and the startups and big companies that want to employ them.

The smart city movement is driven in part by tech-savvy millennials who have different expectations for their communities.

• But for many cities, managing homelessness, hiring teachers and fixing crumbling highways will have to come before developing a smart parking app.

"Younger generations are more demanding of their leaders," said Sameer Sharma, who oversees Intel's smart cities initiatives. "They want governments to be more responsive."

Go deeper:

• Cities are the new data guzzlers
• Cities are writing privacy policies
• The generational gap in surveillance technologies
• The spotty 5G rollout
• The cities no one can afford to live in
• Scooters, cities clash over rider data
• Making cars pay to drive on the roads
• Take-offs and drive-offs
• The race to become "smart cities"
• 3 pictures that explain smart cities

For example: New York's LinkNYC WiFi hotspots, which also have cameras, can analyze images of people passing by particular kiosks. Over time, images could be linked to their identity and other sensitive data, like credit scores.

• Theoretically, that information could then be used to place ads for payday loans around that kiosk, says Katya Abazajian, Open Cities director at the Sunlight Foundation.

If predictions turn out to be true, 5G-connected devices (dashcams, bikes, umbrellas, clothing, keys) and city infrastructure (streetlights, stop signs, utility lines) equipped with elaborate sensor networks will be able to pinpoint your real-time location.

• But the explosion of data and always-connected items will lead to new and unpredictable applications.
• For example, sensors could track how frequently you go to the gym or cameras could see how often you run red lights — data that insurance companies might be interested in, Abazajian said.

The bottom line: "As tech companies get more and more consent from people to collect data on how they live their lives, there are going to be more unexpected uses of that data to shape your access to consumer goods or any services," says Abazajian.

• "It's all about who is sharing the data with whom. And we just don't know that right now."

Go deeper:

• Special report: The human hurdles to smart cities
• The spotty 5G rollout
• The trouble with smart cities
• The cities that have become Big Tech's living labs