Turns out Garmin installation process takes up about 13GB of space for each map.

• Hence neither Garmin MapInstall 4.3.4 nor Garmin MapManager recognize Mk2i. I would like to install OSM Maps on it. The USB mode of Mk2i is currently set to MTP mode and Garmin Express does not work if I set to the USB mode to the only other option, Garmin mode. The USB mode of Mk1 is set to Mass Storage mode.
• Then download the free Garmin MapInstall and MapManager programs. They make installing the maps easy and non-technical. Once you download the map file, open it with your 7z application. It will unzip the files and put them into a folder. After unzipping, you’ll have a few files in the folder.
• MapInstall and MapManager for the Mac. This download area offers free firmware upgrades for select Garmin® units. These upgrades are specific to the specific GPS units and software versions listed. This software should only be uploaded to the unit for which it is intended.

Garmin Express deposits downloads in
%programdata%GarminCoreServiceDownloads

Map Manager is software to annotate and analyze image volume time-series News. We are seeding Map Manager to beta testers, go to the download page to request a copy.; We have a poster at SFN 2018 in San Diego, Sunday PM poster session, Program number 254.17.

The files used by Basecamp to use the maps on your computer are stored in

%programdata%GarminMapsProduct1

Garmin Map Manager App

The latest map for North America is 2017.20 and the Product1 folder is only 2.43GB. I kept the other files in the folder just in case so it is 3.32GB with those in place.

There's a folder for each version of map you choose to keep.

The download folder for 2017.20 was using about 9GB. You do not need the contents in the download folder once you've installed the map on the unit unless you're going to redeploy the map onto a different PC.

I deleted 2016.20 entirely and kept only the installed map for 2017.10. The cleanup freed up 25 GB of space on my HDD.

To get to those folders, hit Windows+R, enter %programdata%Garmin
Make sure you have show hidden folders enabled in 'folder options' (push alt key... select 'tools'... 'folder options')

Garmin Mapmanager 4.3.1

Make sure you're satisfied with the change. The final step frees up the disk space, but you won't be able to roll back once it is done.

Garmin Map Manager For Mac

Control panel > system > system protection
'configure', 'turn off system protection'
This frees up the space. Now, turn it back no so that you have the ability to roll back using system restore for future changes.

I know some one will comment that is nothing because 3TB drives are cheap today, however 25GB is a considerable waste space on a SSD system and wasted time and space on every set of backup you make.