It is my belief that as humans developed the skyward urge and thought of the heavenly realms as a place of light, clouds, golden spires, beautiful blue skies and divine creatures floating by the City came to fruition as an astral location.
If you've ever seen the movie What Dreams May Come, you may remember the heavenly cut-out world in the daughter's room and the landscaped she created in the afterlife - the "seaside" steps and the City in the distance. This too reminds me a great deal of the Celestial City.
People have placed so much hope in the idea of a gold and white place after death. These intense visions have coagulated and made this place that I so often occupy in my thoughts of divinity.