This is not strictly speaking true (full disclosure: was working as an Elixir developer until last year). Elixir/Erlang has quite specialised uses, because it has highly unique characteristics. It does have an excellent web framework, but it simply isn’t as easy to work with as Rails for a number of reasons (smaller community, fewer packages, the extremely specific way that Erlang works, deployments). It looks like Ruby, but how it works is drastically different (which makes some things a lot easier, but other things much harder – Erlang is a compiled language with no mutable state)
Go is something I currently use (we use Go for all our backend services, and I’m busy getting better at writing it). Its sweet spot is small, high performance services – we use it for Lambdas. It’s a good language; it’s very simple, and building things like tooling in it is really quite pleasant. I wouldn’t really say it’s good at what Rails is good at though. It was designed to (and has failed to) replace C/C++ at Google, so that kinda indicates where it sits – it’s designed for lower-level stuff than RoR
This isn’t to say either of these things aren’t good things (personally, Elixir the best language I’ve ever worked with), but Elixir in particular isn’t something that is heavily used. It had a spike of popularity over the last few years, but that’s settled (as has the language, it’s basically feature complete). It will probably stay at that low level, quietly powering things that require what it provides (networks of IoT stuff for example), as there is no killer app. It has some exceptional characteristics, but most people simply don’t need them. Go is relatively heavily used because it has a killer app driving adoption (Kubernetes), although usage is small compared to the more popular languages. Go is primarily a systems language, Elixir is for [complex systems of] things that not go down no matter what, Ruby is a high-level general purpose language
Ruby’s killer app is RoR, and yes, less people are using it, and yes Ruby is becoming less relevant, but it’s still excellent.
If you want to build something quickly, I would say yes. Django is another option, and the vast wealth of Python libraries available may be useful to you for what you want. As I say though, spatial data is possibly more dependent on things that aren’t specific to the web framework – for example the database you use is probably going to be more important (Postgres for example with spacial data extensions). I don’t know much about this area, so can’t comment much beyond that tho
