We have explored a few ways to allow more detailed control of the in game map internally, and we can’t speak to where those plans fall on our roadmap right now.
In case your were curious and wanted to try and get a little more control over the map until we release improvements, we currently create a bounding box of all the Actors in your map, and try to use that information to determine the bounds of your level. We have a limit set right now that caps it to a radius of 61,000. If you work within that radius, and make sure no actors have extraneous scale or meshes causing them to be huge, you can get the map to draw rather nicely around your island.
Here is an example of the Blank Map project template and changing the bounds of where it draws.
This is what the map looks like without any changes.
If I select the 4 grid plans and delete them, after pushing changes now the map is much smaller and just shows the two player spawn pads!
I added the castle keep prefab from the Prefabs section using the Phone Tool and pushed changes you can see the map grew back in size a little bit, showing the Spawn pads, and the caste keep now!
I hope this information helps you out!