I'm not sure where to set this value, but it's extremely noticeable when the value defaults to -7 and you go and place a node and it looks like a colorful square smaller than your fingernail.
I tried a few different templates and noticed these zoom values:
First Person: -4
Third Person: 1:1
Top Down: -7
The zoom value for the Level Blueprint differs from template to template. More often than not, the value is not 1:1. This causes any nodes you place to look tiny and unreadable.
Level Blueprint for all projects opens with a zoom value of 1:1
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-41263 in the post.