ZLC Controller voiced concern regarding the poorly marked MIA depictions on various types of equipment and charts; indicating the conditions were a factor in the weather deviation event described in this report.

Narrative

I was training a developmental on R47/45. Aircraft X was Westbound in our sector at 140 from ILC-KROST-MVA and landing RNO. Just East of Krost; Aircraft X requested a routing change direct OAL YERIN RNO due to weather he was looking at over MVA. At this point; the sector frequency was very congested due to bad rides at higher altitudes. As the trainer and due to frequency congestion; I took over communication of Aircraft X. Since we were having Westbound high altitude traffic deviating North of OAL; I explained to Aircraft X that there was weather over OAL and that a heading of about 260 to go between MVA and OAL looked to be the best option. The pilot agreed. I assigned heading 260 to Aircraft X. A few moments later; Aircraft X said there was weather right ahead and that the heading of 260 might not work. I cleared Aircraft X to deviate right or left and to maintain 140. As we were handing off the aircraft to ZOA46; Aircraft X requested descent to 120. We took the hand off back and the D-Side coordinated this descent with ZOA. The D-Side said that ZOA46 denied this descent because of what I thought was an MIA of 140 just North of the aircraft's track and on the ZLC/ZOA boundary because Aircraft X had approval to deviate North. I asked the D-Side to ask ZOA if we assigned Aircraft X a heading to stay South of that 140 MIA; would they approve the descent to 120. After coordination; I was told descent approved. I assigned a heading of 255 or South to Aircraft X and issued descent to 120. When Aircraft X began descent; we got an MSAW alert of 139. The 139 MIA that the aircraft was transitioning is depicted very poorly on both the RADAR scope; MIA polygons and on the overhead charts. On the overhead chart; the 139 MIA is depicted well North of the sector boundary between ZLC Sectors 47 and 43 and on the scope; the 139 altitude is depicted North of the Sector 47/43 boundary. There is also a sliver of 130 MIA airspace adjacent to this 139 MIA on the East side; which is misleading. Also; the red center/sector boundary lines on the overhead charts separate multiple MIA polygons; which visually misleads with a sector boundary line running through the center of this particular MIA. If sector/center boundary lines dissect MIA polygons; the MIA altitude should be depicted in the affected MIA areas.