Super King Air 200
Air Traffic Control Fully Certified
Confusion; Human-Machine Interface
ATC Issue All Types; Airspace Violation All Types; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter CFTT / CFIT
Air Traffic Control Issued New Clearance
ATC Equipment / Nav Facility / Buildings; Airspace Structure
Aircraft X was handed off to me from ZOA 42; with RNAV 29 in the 4th line. The aircraft was direct PLYAT the IAF for the approach and checked on with the weather and again requested it. Due to the odd angle; how deep into ZOA the aircraft was; as well as fact the scope was set up for the midshift; I used a nearby scope to zoom in to the area. I double checked the crossing restriction altitude as the MIA (Minimum IFR Altitude) lines in that area are somewhat confusing and issued a crossing restriction of 7;600 feet. (which is the MIA that PLYAT is in).Immediately south of that is a weird little carve out; that is attached to another MIA that runs up the eastern side of the sector. The small carve out has no MIA label on the video map. When I checked for the crossing restriction; I ran the route line and pulled up the MIA map on the adjacent scope; noting the highest MIA that I saw (7;600 feet.) which was subsequently issued.I did not realize until the MSAW alerted that the aircraft was going to violate the MIA. At the same time as this was happening; I was also sequencing aircraft at MFR and noticed some flashing in the ACV area. As this is an area that we routinely get false MSAW alerts in; I put it out my scan and focused on the other aircraft. I finally noticed the MSAW alert for Aircraft X when they were about 8;500 feet. and descending; however due to an incorrect transmitter selected; and then poor communications in that area; I was unable to issue a stop in time before the aircraft violated the MIA. By the time I issued the correct altitude the aircraft was already level at 7;600 feet.; and the next radar hit took them out of the MIA; due the timing and the few seconds the aircraft was in the incorrect MIA; I did not issue a low altitude alert. I would suggest that the MIAs in that area be redrawn as to make them less confusing; and/or at least label the small carve out that is attached to the other MIA. In addition more work needs to be done with that specific transmitter as it has been an issue for many years and aircraft that we should have good communication with is often times difficult.
ZSE Controller reported BE20 entering a higher MIA due to MIA map being difficult to read on mid-shift scale.