I disagree. I believe cartographers should be permitted to submit their own work for consideration. Call it a "submission" instead of a "nomination," to reduce the sense that you're patting yourself on the back.

Otherwise, you're only likely to get entries that are fresh in peoples' minds at the time nominations open, leaving out work that was made early in the year or after nominations were opened. (This is part of the reason we have "Oscars Season").

If someone works specifically toward this award all year only to not get nominated because they weren't permitted to submit their own work, that could leave a very sour taste in their mouth.

Finally, we already have a nomination system in place with the Cartographer's Choice award.

edit: And by the way, productions do nominate themselves for many awards, such as the Emmys and VES Awards.