Hi @_simon - Welcome to the community
In general, if you keep your application deployment within the same region as your Atlas deployment, it would be closer (in network/region terms) to the Atlas deployment compared to an application in a different region or cloud provider.
which I believe can’t be deployed on the same infrastructure as my MongoDB Atlas database.
If you are referring to the same hardware/VM’s in which the Atlas clusters are hosted, you are correct as Atlas is a managed service.
What are people doing to keep their application(s) as close to their MongoDB Atlas database as possible (in order to reduce latency)?
More details regarding cloud provider availability and regions for Atlas can be found here. However, in saying so, if you’re already hosting your application on a particular cloud provider on a certain region, you should generally be choosing the same region and cloud provider for the Atlas cluster. Of course this will depend on each use case / requirement(s).
If your application spans across the globe, I would perhaps go over the Manage Global Clusters documentation as well.