I am working on a project which requires the use of a boost converter to power a sensor which is read by a microcontroller. Both are powered from a battery. I know that when reading signals from a different device their grounds must be joined. That made me wonder if boost converters change what common ground is. I believe transformers do but these aren't the same thing. Looking at their schematics I would guess not but I want to be sure.
There are isolated converters and non-isolated converters. Most are non-isolated converters. The module description or the circuit design description will tell you which it is. Usually they are non-isolating.
The output from an isolated converter will have a separate ground from its input. That lets you do fun things like connect the positive from the output to the ground of the rest of the circuit to generate a negative voltage (that kind of trick, of course, breaks the isolation.)
Isolated modules usually cost more and are a little more complicated to build. They have separate current loops for the input and the output sides. They often use transformers to galvanically separate the two loops.
Most common circuits and modules are non-isolated types. The ground on their input is connected to the ground of the output. They usually don't contain a transformer. There's a switched inductor, but no transformer. You can build a non-isolated converter with a transformer, and some circuits and modules do so.
With an isolated type, you would have to intentionally tie the grounds of your circuit together to, for example, measure the output voltage. That is much like what happens when you use a simple AC transformer.