Bottle City

A Bottle City is an abducted location, miniaturized and stored within a life-sustaining "bottle" by Brainiac for the purpose of study and analysis. Once he has obtained all that he wishes to know, Brainiac can extinguish the bottle's life-support systems and digitize the bottle's contents to be reused at a later date to house another abducted location.

Background
Using his advanced understanding of mechanical engineering, bio-engineering, physics, and other theoretical and applied sciences, as well as extensive knowledge of various alien technologies, Brainiac is able to create various force fields the likes of which can not be penetrated even by Superman.

Utilising these force fields, Brainiac has formed a strategy where he erects such fields around locations on target worlds and forcibly removes them from their foundations for the purpose of miniaturisation and study onboard his ship. This practise usually proceeds the destruction of the target planet. This abducted locations are later stored in life-sustaining jars, becoming "bottled cities".

Trivia

 * Kandor was once the capital of Krypton until it was shrunken and stolen by Brainiac several years before the planet was destroyed. Superman discovered the city in Brainiac's possession when the android came to Earth decades later to harvest more cities and rescued it, keeping it in his Fortress of Solitude while looking for a way to restore it to full size.