Here's how I categorize different stages of financial health: struggling, getting by, comfortable, well-off, rich, ultra-rich.
Without attaching a specific number to each category, I'd say that the biggest differentiator between one category and the next is your disposable income: net income - necessary expenses (rent, food, utilities, transportation, debt).
When you're struggling, your net income can barely keep up with your necessary expenses, and so you have zero or even negative disposable income. You might have to juggle between which bills to pay, or have to go into debt to keep up with your expenses. When you're getting by, your net income is somewhat bigger than your necessary expenses; you're able to save up for certain luxuries, but it will probably take you a while. And any unforeseen expenses take you back to square one.
When you have enough disposable income left over that you can regularly afford to treat yourself to some luxuries, maybe afford a vacation once a year, and put some money away toward retirement, then you're comfortable. When you have enough disposable income to fully fund your retirement, can afford most luxuries attainable to regular people (so no Lamborghinis), can afford to go on 2 or 3 vacations a year, and still have some money left over, then you're well-off.
I'd say that someone making $100k in San Francisco is probably just comfortable. Their net income is certainly much lower than $100k when you take taxes into account, and their necessary expenses are all much higher than the national average.
fivethirtyeight.com
www.motherjones.com
