Within most class B areas there are several busy D airports. For example in Minneapolis you have STP, FCM, ANE, MIC. When tracking flights it would be helpful to create a ZMP.
I just did a search from each of the MSP area airports to ZNY and they all had flights.
I’m sure this is the same for other areas like DEN, DTW, etc.
You can use the center codes in the Flight Finder, but no where else.
When you type in JFK, it gives you the option of “New York Area” or if you type LAX it gives you the option of “LA Area.” I’m suggesting that the “Area” option is available to other cities, such as MSP, DEN, etc.
DTW too.
ZMP added (will take effect tomorrow, we’re still dealing with higher than normal load due to the 787 flight), please provide a list of ICAO airport codes for the other areas you’d like.
Pretty much any class B area would work.
Just off the top of my head…
MSP - FCM, ANE, STP, MIC
DEN - APA, BJC, FTG
DTW - YIP, ARB, PTK, MTC, DET
Any users with other locations feel free to contribute…
DAL & DFW etc
I believe that is ZFW.
I believe you are correct. Thanks! 
ZDV and ZDT (unfortuantely they fall under Cleveland Center so I made one up) added. Will take effect in an hour or so.