Level designers' collaboration

We work in a small team: 2 developers and 2 artists, and we use Git as source control.

We found that level file (.umap) that we are working on has binary format. So if we edit this file simultaneously, it will be impossible for us to merge our work with using of regular merging tools (because .umap is binary).

Are there any common techniques or best practices to resolve or workaround this problem?

Any help will be appreciated. Thanks.