Air Traffic Control Fully Certified
Air Traffic Control Time Certified In Pos 1 (yrs) 16
Human-Machine Interface; Situational Awareness
ATC Issue All Types; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter CFTT / CFIT
Air Traffic Control Issued New Clearance
Airspace Structure; Human Factors
Aircraft X was being vectored for a visual approach to ZZZ; a satellite airport in the Bozeman sector. He was level at 13000 [ft]. My airspace boundary map and my MVA map were set at the same intensity so I mistakenly thought he was in a 12000 MVA so I assigned 12000. 30 seconds later I realized that he was still in a 13000 MVA so I reassigned 13000 but he had already started a descent. Instead of climbing back to 13000 (he was about 12500) he called the airport in sight and I cleared him for a visual approach. I am going to change the intensity settings on my MVA map and my airspace boundary map so that the lines don't look the same and it will be clearer what the MVA is.
BOI controller reported a BE20 was descended into a higher MVA.