Actually this is a very good question for engineers, as the (wrong) idea that a smartphone regularly sends data to a satellite shows fundamental lack of knowledge in some very basic physical understanding. The basic understanding should be: transmitting/sending = emitting energy (costly if a device runs on batteries), receiving/listening for a signal = almost for free nowadays.

I also like the question because even if you have no idea how GPS actually works, you could quickly come up with the rough idea yourself given that you have a bunch of satellites that can emit arbitrary signals. Lots of room to show creative and analytical thinking here.

> Actually this is a very good question for engineers

What kind of engineers are you interviewing?

> I also like the question because even if you have no idea how GPS actually works, you could quickly come up with the rough idea yourself given that you have a bunch of satellites that can emit arbitrary signals.

I find this really doubtful. Someone who doesn’t already understand how GPS works is unlikely to derive it from first principals in a brief interview.

If you make some simplifications and assumptions such as a GPS receiver has a highly-precise & synchronized clock (it doesnt), you can conceive GPS basically as a system where each satellite simply broadcasts its position & own current timestamp and then determining your position of the earth surface becomes basic triangulation calculating the time-in-flight of the received signal from multiple satellites. Of course a lot of simplifications in there (such as constant signal expansion time), but I would say a system that you could design with basic geometry. The required knowledge is basic physics and math that everybody calling themselves engineers should have heard at uni (or even at school).

You’re still going to wind up assuming a lot of baseline common knowledge that, while it might be stuff you find interesting and have come across in pursuit of your personal brand of geekery, are likely not actually necessary for the job.

Just consider that there are people - perfectly intelligent, capable of learning - who don’t actually know what ‘GPS’ stands for. They maybe don’t know that the GPS system is separate from their phone’s cell connection. They may not even know that satellites are involved. They may have not taken enough of an interest in space technology to have internalized how satellite orbits work, to have intuitions for how orbital speeds and altitudes are correlated. Or they may have picked up a common misconception at some point in the past about how cellphones work, thinking cellphones are always talking to satellites. So they might have made some reasonable intuitions about how GPS works that - because they haven’t been exposed to the true answer - cause them to make some erroneous assumptions that seem like dumb mistakes a poor engineer would make.

Not having had the opportunity to come across those things is not the same thing as not being able to incorporate that knowledge into your worldview when you encounter it.

Ok, but feeding the candidate half of the information is pretty different from coming up with the rough design with “no idea” how it works. Yes, if you basically tell them how it should work, then they can probably figure out how to calculate the time difference and do some trig.

I mean if the candidate would insist that the smartphone sends a signal to the satellite, you can go on and ask "what kind of data?" -"Nothing, just a PING to which the satellite answers with a PONG that contains its position". This is not at all how GPS works, but this system would also work (in a sense you could determine your position on earth based on the RTT + transmitted satellite coordinate). It is not that the candidate should come up with a perfectly correct solution (actually this could be bad because he could just blindly repeat what he/she read without understanding it) - its whether he/she can come up with a solution for the problem at all. In the interview you could still go into discussion about that approach then (what about undirected energy dissipation for contacting a thousands-of-km away satellite, and problems with time-multiplexing transmissions now on the satellite that has to answer individual requests vs broadcast etc.).

I have a hard time imagining engineers in any other field (e.g a structural engineer) would be getting asked questions about GPS as a proxy for general engineering knowhow.

Do you have experience interviewing or seeing interview questions in those fields?

Yes, you will be asked to showcase 2-3 side-projects such as houses, bridges and tunnels you built & designed in your backyard and discuss your design decisions on a whiteboard.

Maybe a take-home exercise, like a small viaduct or a dome.

Not sure if serious?

Some are silly, some are effective ways to measure curiosity and ability to think through an abstract problem.

Yes, but how many of them are relevant to determining if a particular candidate is a good fit for a programming position?

Well, obviously if the candidate is round then they fit.

or was that the pothole cover? Sorry, I might have gotten confused.

Engineers, not programmers.

What kind of “engineers”? I’m not aware of most engineers going through this sort of interview. Mostly just software engineers who are indeed programmers even if they get uppity about the title

OK, I'll play. Some qualities that are valuable in an engineer are curiosity, creativity, and general knowledge. If your nomenclature has a programmer as a software engineer and a software engineer as an engineer, then these qualities are also valuable in programmers.

If you ask an interviewee how GPS works and he says something about the cell phone sending signals to a satellite, you would want to pursue that further, at least to make sure that he's asserting that with a sufficiently low confidence.

Let me rephrase my question.

Are you nitpicking the difference between a different engineer and a programmer or are you interviewing a different sort of engineer?

The thread became about whether a good interview question for an engineer was how she thought GPS works. HeyLaughingBoy thinks that the qualities a question like that seeks to explore are irrelevant for a programming job.

I think that it is a good question for any engineer. One explanation for why HeyLaughingBoy might have disagreed was that HeyLaughingBoy was making a distinction between a programmer and an engineer.

I thought that highlighting the distinction between what HeyLaughingBoy wrote (programmer) and the parent (engineer) was a parsimonious way of expressing this.