Until we can get commissions from someone like WotC, its unlikely any of us will see a map income that equates to our day jobs, which is one of the reasons I'm getting into publication. Not the only reason, of course, I like to create settings, mechanics, new classes, new spells and create storylines as much as I enjoy creating maps - I just have more talent with the latter than the former.
Since I can craft all my own maps for my own publications, I can do what hiring publishers cannot - afford many maps in a given publication, as most publishers generally can only afford 1 to 3 maps in most cases. My first adventure has 12 maps in it, mostly encounter scale for specific places in the storyline. This way, like a publisher, I am building my map cost into the overall product and it will be paid for with overall sales of the product rather than limited commission payment from a publisher. Note you are paid faster doing commissions than product sales however, but you can't make the kind of money on a commission that a successful product can earn. (It has to be a success though, or you might only break even.)
Although not getting me rich, my first adventure has earned about $600 in total so far, and it cost me about $175 to produce, so its paid for itself and provided some profit - and the sales aren't complete, but may go on as trickle income in perpetude. So I think I'm following the right course for my goals.
I still do commission work, but since I am currently involved in two publications and am now working on a second setting of mine, thus a third publication in the works, I have much less time to do third party commissions, and am not so concerned with that anymore.
Its fun that I get paid for doing what I love, but unfortunately it currently hasn't been able to replace my day job - a goal, that I like many, have.
GP