Question

If a scale of the solar system was built where 1 mm equaled 1 mile, could the model be practically built in a city?

Answer 1

No, it couldn't be.
On that scale, Neptune would be almost 1,740 MILES from the sun.
ON THAT SCALE !

Answer 2

No

Step-by-step explanation:

Given the relative scale (1mm = 1mile) lets calculate the size of the Sun and distance of planets from the Sun in mm.

Diameter of Sun = 864938 miles = 864938 mm = 864.938 meters

Distance of Earth from the Sun = 92955810 miles = 92955810 mm = 92.955 km = 57.75 miles

Distance of Jupiter from Sun = 480000000 miles = 480000000 mm = 480 km = 298 miles

As can be seen, the magnitude of scaled down distances is too huge to fit inside a city.

It will not be practically possible to make such a model.