Hello, pureblur,
Thanks for using Apple Support Communities, it's great to have you here. We understand that Maps is working in the background and you'd like to prevent that from happening if possible? We're happy to help go over any options available here.
Do you use iCloud to sync data between your Mac and any other Apple devices you use, or even just to the iCloud website? If so, it is possible that the extra usage you're seeing is simply Maps syncing with iCloud periodically to make sure things like your favorite places are up to date. To check if that may be the cause, you could open up Maps and click "Maps > Account" in the menu bar. If you are currently signed in to your Apple ID, you could simply sign out and then keep an eye on the Activity Monitor for any changes.
If that seems to be the cause of the issue, it would be totally up to you if you'd like to continue utilizing that feature or if you'd prefer to disable it.
If that doesn't do the trick, however, then we would recommend that you try booting into safe mode. From safe mode, see if you can recreate the issue with Maps. Safe mode disables a number of startup items and runs macOS in a limited mode, so testing the issue in this manner can help isolate the root cause of the issue. This article will help you boot into safe mode: Start up your Mac in safe mode - Apple Support
Let us know what you see!
Cheers.
