The answer is quite obviously planet Earth, or Sol III. Come on gimmie a tough one.
In all honestly though I want to say that synthpop evolved from an era where the UK had kind of the resources and one of the first kind of "electronic music" studios, the [correction: BBC Radiophonic workshopdunno why I said polyphonic radio]. I'm sure people all over Europe and the UK had "futuristic" ideas of what music was going to become, and tons of work was being sent to the BBCRW from all over the area. (I was mainly interested in what the Netherlands was sending them - fantastic tape works from )
I want to say that synthpop is an era where analog synthesis was hitting it's prime and digital synthesis was coming into it's own "musique-concrete" era. Now, don't quote me on that. I'm no historian, but have looked briefly into those eras before for their tonal aesthetics.
I will say without a doubt that musical culture is something we all contribute to, it seems vain to assume that any one genre of music (or any art, or philosophy for that matter) originated in a region even though it's quite obvious some do belong to particular regions.
For instance: the divide between Traditional Western and Asian musics, is confined culturally and chronologically. However, we can't assume that someone living with traditional Asian compositional aesthetic never had thought of what "defines" traditional Western composition (or vice-versa).
I like that a lot of electronic music tends to be based more on a prediction of a time and place, rather than defining a time and place. Music is a kind of universal communication for us, where the cultural divide between words can fail, music is the language.
I ask for a specific country cuz I have a series made up of various EDM genres as humans, and most of their bios state that they originate from 1 nation -- a couple of characters I have only jotted down more than one country origin because they were a more worldwide type of genre (such as Eurodance, Dark Ambient, Spacesynth...)
if Synthpop is one of those kinds of genres that people in various countries have thought up their own sounds for in the same era (but all called it "synthpop" music)... then I will make him originate from both Germany & the UK (unless there are also other countries that are known for making synthpop~)
I see! Well, in that case I will say it doesn't matter where someone is from when it comes to what music they are writing.
For story's sake I will say synthpop is more "accepted" in Europe and the UK, whereas here in Canada and more in the US it tends to be ridiculed - and tends to be darker because of that (Industial/EBM).
Yeah, if you want the characters to have an easier life as synthpop musicians, I would say you are safe putting them in the UK or Europe (like Germany or the Netherlands - HUGE electronic pop scene in Holland!)