Originally Posted by MSPeconomist

San Diego also has a cluster of high income people.

You might be correct about the distribution of the FF population in general and high income individuals, but FFers in different locations are more or less likely to fly DL depending on where they live. For instance, DL doesn't have a hub or much nonstop service from the Bay Area, so high income FFers aren't very likely to use DL as their primary or even secondary program. The same is true for the LA area, although less so since DL has more service at LAX than SFO. Similarly, in NYC, DL is increasing its presence, presumably with more (high income) FFers, but many of them focus on AA/US or UA/CO, especially if EWR is more convenient for them (which would include all of the Jersey suburbs as well as at least parts of lower Manhattan).

By contrast, DL FFers are more likely to be concentrated, relative to the population of FFers in general, around DL's hubs and focus cities, such as ATL, SLC, MSP, DTW, CVG, SEA, MEM, IND, BOS, RDU, TPA, PDX, etc.

For discretionary spending on premium cabin air travel, what probably matters is not absolute per capita or family income but some measure of discretionary income after taxes relative to the local cost of living. These adjustments would knock down "income" data for California and New York substantially.