I run a small press RPG publishing company, Misfit Studios. I currently have a relationship with several artists whereby I sell their art through my storefronts as licensable (aka "stock") art. The art is sold so gamers can use them in their gaming material or publishers can use them in products. After doing this for several months, I thought that cartographers may similarly be interested in commercializing some of their maps. So, here's the breakdown on the arrangement I currently have with the illustrators and am looking to extend to cartographers:

Selling Locations
The primary locations where I sell my digital products are:
RPGNow (the world's biggest digital RPG online store): RPGNow.com - Misfit Studios - The Leading Source for Indie RPGs
Misfit Studios: http://www.misfit-studios.com/store/

I am considering extending the art sales into the other storefronts I use. The reason I've not done so yet is they are not really focused on selling publisher resources, such as licensable art.

What You Bring to the Table
-Your professional quality cartography, symbol making ability, etc.

What I Bring to the Table
Misfit Studios has been operating as a small press publishers since 2003. We have an established market and regular, ongoing customer base. This means we have people who pay attention to our blog, etc. to keep track of our releases. All art is sold with the Misfit Studios branding. This is one of the advantages of selling through us instead of doing it yourself -- not only do you not have to worry about bookkeeping and the like, but you don't have to worry about building a reputation and getting people interested in your product from ground zero. People know who we are, our products have a good reputation, and you get to benefit from that branding.

We don't push your product merely as a Misfit Studios product, however. If you look at our blog, you will see that we focus on pushing the artist and their skill to the forefront, putting the art and the talent behind it into the spotlight.
Triple Art Release from Eric Lofgren | Misfits In Action: The Blog

Here is an example of cross-promoting an artist release with one of Misfit Studios RPG releases to increase the former's marketability: A Double Shot of Zombie Goodness with Stock Art and the Return of Your World No Longer

I also have a Zazzle merchandise storefront if you want to try putting your maps on mousepads or the like.

The Product
-I'm looking to sell maps, floorplans, symbols, symbol catalogues, etc.
-If you're also an illustrator, I can sell those on your behalf, too
-The images are sold as 300 dpi files; the more file options you have (vectors as well as rasters, for example), the more appealing your product has to customers
-you produce on your schedule; the more product you make available, the greater your chance of making money. Larger catalogues cast a wider net.

Pricing & Payment
-You are free to set whatever price you like
-I (Misfit Studios) keep 5% of the selling price; this means I only make money if you're making money
-All payments are a percentage of the selling price; you get whatever is left after my 5% and whatever the storefront takes. For example, RPGNow takes 35%, for example, so that would mean you would get 60% of the selling price. e23 keeps 20%, so you would retain 75%. Because it's my storefront, the Misfit Studios store only retains my 5%, so you would make 95% per sale (or 85% or 80% if customers use existing coupons in circulation.)
-Payments are made monthly via Paypal so long as you have made at least $10 in sales that month. If not, previous months accumulate until at least $10 is made. (If you run into an emergency, you can contact me to get paid earlier, if possible.)

-Cartographers retain full ownership of all maps/symbols/artwork; you are granting a limited license for others to publish the map
-anyone using your maps/symbols is required to post your copyright in their product and list you in the credits. If you have a website you use for promoting your maps, we can also require a link to the site be provided in the credits.
-If I like a specific piece, I cannot just use it -- Misfit Studios is bound by the license, just like everyone else, and the fact that I am essentially acting as your agent for the map's sale does not give me free use of it. In fact, because there is no intermediary, I'll pay you full price of any maps or symbols I want to use in my own project without keeping my usual commission.
-I can provide samples of the licenses via email, if you like. If there aspects you don't like, we can discuss to make changes to make you happy, although I will provide feedback based on my experience selling art and as a publisher to let you know if the changes you want to make will be detrimental to your ability to sell product. Not all of the artists currently selling through me use the same license, for instance.

-The license I create on your behalf also lists your contact info so that, if the customer likes what they see, they can contact you directly for custom work
-Each of your releases is announced through my social media (Misfit Studios has a blog, FB page, G+, and Twitter), as well as posting it in relevant gaming sites. All posts have links directly to the product page for "one click" purchasing
-To provide you with personal branding, each cartographer is given their own product category on the storefronts, when this option is available.

The artists I am currently selling art for are all listed on my RPGNow and Misfit Studios site. I encourage you to contact them about their relationship with me selling art on their behalf -- some of them sell well, and others not as well because of their limited catalogue or the content only appeals to a small portion of the market. If you contact Eric Lofgren, you can also ask him about the royalty-based projects he has with Misfit Studios.

Potential Misfit Studios Royalty-Based Projects
Additionally, I am considering selling some specific symbol catalogues for a largely untapped super-heroes and horror genres. I have plenty of ideas, but am not an illustrator. If anyone is interested in helping me with this, I bring the above to the mix, as well as enough digital colouring ability to handle symbols (I currently colour many of my RPG products' interior illustrations.) Such a project would be a 50/50 split of all profits made, and participants would also be free to use the resulting symbols in their own mapmaking projects.