There are software that works like this (e.g. a website's unrelated pages and their logic), but in general composing simple functions can result in vastly non-proportional complexity. (The usual example is having a simple loop, and a simple conditional, where you can easily encode Goldbach or Collatz)

E.g. you write a runtime with a garbage collector and a JIT compiler. What is your map? You can't really zoom in on the district for the GC, because on every other street there you have a portal opening to another street on the JIT district, which have portals to the ISS where you don't even have gravity.

And if you think this might be a contrived example and not everyone is writing JIT-ted runtimes, something like a banking app with special logging requirements (cross cutting concerns) sits somewhere between these two extremes.