When writing in a setting beyond personal experience, research and exploration can steal months or more. Whether it’s a real location or one that’s come from the imagination, there is always more that could be known.
This is an aside to what makes it into the written drafts. To some extent, even the places known to the writer require research and fact-checking.
The sense of wonder that a location can hold is equally as important as the credibility of its portrayal. This isn’t the concept of everywhere being special, though there is a touch of that too. It’s critical to present a coherent front, or initial impression of the location. The weather is a factor. The scale is a factor. The landscape and vegetation are factors. What types of buildings are present, what they are made from and what their condition is, it’s all important. It’s important for the fauna of an alien planet, and for a city considered home.
The elements of the location that are there in the imagination create a sense of a place beyond the visual details, and while they inform the writing process and do bleed into what is written, the details are often so presumed as implicit that they go unstated.
If the reader knows the location, they may be able to assume a reasonable approximation. If it isn’t known, those unstated details will leave the setting in an unfinished state.
It might not matter. The bare minimum allows a reader to substitute your nondescript cities with ones known to them. They may picture Edinburgh, Madrid or Boston, depending on their experiences, and the small notes of character that do make it onto the page.
It’s no different to characters, where a terse description of a muscled bald man with bad teeth is enough for some reader to picture a character. In some cases, the identity of the character matters more. The protagonist in these cases is not a surrogate for the reader, but are intended to be someone distinct. Sometimes it is purely because that’s how the character was first imagined, and it’s how their image should be shared.
Locations can have the same need. They’re pictured as a specific location, and have a distinct feeling that builds on the narrative in specific ways. In a story about oppression, a claustrophobic city will have a different feeling to an open, expansive one. The beauty of a location could be an intended dichotomy, or the destitute and decaying environment may be a means of reflecting a rotten core. A reliance on implied details for a location could mean that the narrative is either not as effective as it could be, or that it does not carry the imagery intended by the writer.
There are constants that can be assumed by virtue of the generalisation of the location. A forest is expected to have trees. A city should have a large number of buildings or structures, with the expectation of a population. An abandoned city qualifies that further, as a subterranean city also would. The abandoned city might be decayed, wartorn, or pristine. Individual areas within the location may differ.
The weather is a factor, and how the location reacts to either rain, wind, sun or snow matters. There should be reasons why it is in the condition that it is, including why it is abandoned. Sound matters. Smell matters. Beyond the senses (assuming that the characters won’t be licking brick walls), a location needs a statement of its activity.
If a character was to walk through the location, how would they react? Would they feel safe? What characters would, and which wouldn’t? If they had an hour to kill, what could they do? If there was a sealed envelope found on the ground or floor, what might be in it? What lives had come and gone before the characters arrived there? Is the climate harsh? Enjoyable? What effect does it have on their energy, their comfort, their skin and their clothing? Do they need to dress differently? Where in the location could a character go to observe a view? Would they consider it pleasant or beautiful, or would it fill them with dread? Is it by a river or sea, a concrete jungle or one of vegetation?
Beyond that and back to one that has crowds or background, how does the overall theme of the location manifest in the denizens we’re not concerned with. In what ways do the ideals of the location permeate through the living elements that interact with the characters? What do they do with their lives, and if there is danger in the location, how have they persisted for so long? Are they happy? If not, why are they there?
Consider these questions and whatever else arises to build a more precise set of details about the story’s location. Not all facets will be used, though having more knowns about a location will lead to details organically appearing in successive drafts. It will also steer location descriptions closer to consistency, which lends realism to the world portrayed.
Sometimes the picture may still need to be explicitly painted, to give the reader the details that cannot be implied.