Can we cite a source from another field of study?

Actually it is probably required. If you use ideas from any source you need to cite them to avoid plagiarism.

Your field has many interdisciplinary elements in any case. Just. Do. It.

Yes and it is more common than you would think.

Let's think about marketing. Marketing falls, broadly speaking under the umbrella of economics (at least at a lot of universities). Many of marketing's most important findings were based on findings in the field of psychology, so a lot of papers written in the general field of marketing cite psychology sources.

Biologist cite physics sources.

Medicine cites physics sources (Something with blood gas exchange, my girlfriend has to learn this stuff currently)

Computer science, especially when concerning quantum computing, cites physics.

Medicine cites psychology and vice versa.

And we could probably find a lot more.

As you can see. There are plenty cases where this is ubiquitous. So, please cite your sources ;)

Edit: I almost forgot that during my master thesis I had to cite a medical source when I was researching the term security hygiene.

Fields aren't a walled-in, hard, definite thing

Fields are a vague direction of topics, with precise (and closed) definitions being made up by different entities in different ways. Journals focusing on one field will have their definition. A university will have a potentially different one for their departments.

Take Marketing (thanks Eomer) for example. It's neither (pure) economics nor is it (pure) psychology. And it's papers often enough fall into the domain of sociology.

Yes, universities and journals will place it squarely into one or the other field, but that is because they need one definite answer for organisational reasons, not because that is the one true answer.

The Venn diagram of what's what field probably has more overlapping than "pure" area.

This is not to say that fields aren't a helpful concept

Most fields have their own methodologies, terms, assumptions and assertions, with some words being different terms determined by the context of the field they're used in (like "ring" in archeology (it's just a ring) vs math (nobody outside math would call that a ring)). If your work intersects multiple fields in such a way where the intended meaning of some terms isn't clear, explainers, footnotes etc. are necessary.

Why am I taking this detour?

Your question asks about "referencing other fields" as if it were some frowned-upon exception, something you shouldn't do except when absolutely necessary. But the opposite is the case: Cross-discipline works and references are incredibly important to scientific progress and should be done whenever it's helpful. You do use statistics after all, don't you?

What to consider when "crossing into other fields":

• how you (and your readers) interpret certain words vs the intended meaning (both from you and your source)
• make sure that you understand the assumptions and assertions made in what you're citing. (Sometimes this is obvious, sometimes it's not)

[Not 100% applicable to your specific case:] When writing an intersectional paper, consider lowering your requirements of the readers knowledge on any subject specific things because it's quite likely that a reader coming from field A will not intuitively know the same stuff as someone (you?) coming from subject B.

Your paper isn't (from what I can tell) that intersectional in output. All you want to do is take a method and apply it in a different context, but the output is staying within Urban Planning as a whole.

Not only is it allowed, it's necessary. I doubt you'll find a single objection to it anywhere. Actually, interdisciplinary work is something you can brag about on your CV. In the course of one of my projects (in zoology), I had to extensively cite papers on physics, specifically aerodynamics. It was a headache to get into the weeds of that field, yes, but my research wouldn't have been complete without it.