Field Mapping provides a map to import metadata about the media type.
Looking in both the Height and Width fields, we find that they don't have corresponding select entries.
This means we need to add them into the media entity type.
To add a new field:
Click on the Manage Fields tab.
Click the Add Field button.
Add a New Field select box = Number (integer)
Label field = Width
Machine-Readable Name field = override to media_image_width
Click the Save and Continue button.
A new screen will appear.
Allowed Number of Values drop down fields = Leave as is
Click the Save Field Settings button.
You'll be redirected back to the field list with a new Width field displaying in the list.
Now click the Add Field button and add a Height field using the same method that was just used for Width.
After the Height field is added, you'll be redirected back to the Manage Fields list.
Your new Height field will show in the list.
Now it's time to map those new fields.
Click on the Edit tab.
Click the Save button.
Upon saving, you'll be redirected back to the Media Types screen and will receive a confirmation at the top.