Knowing that people have different things going on in their lives, and while a week technically should be enough if one can dedicate all your time that week, most people won't be able to do that. My suggestion is just do a month, run the entire month of May for example. This means you can take a few days and think up a proper announcement post. Take the feedback gained here (perhaps more will come) and then write up a new topic, declaring the challenge and explain the rules (hint: try to be focued, but not overly strict. A common theme to give people ideas and compete in the same space is fine, but too strict rules scares people of (ref the usage discussion above)).

I can then give that topic a temporary sticky status for the duration of the challenge.

If anyone wants to arrange such a challenge, feel free to do so. While I don't have the skills required, I'd love to see a competition going on for those that have, and maybe there will be some nice results for everyone to use.

But I think Shessar is right. If you force a specific style, you will be excluding lots of otherwise skilled people. While the symbols produced will be less usable overall because they don't have a single style, it wil allow everyone involved to do their best instead of being forced to try to emulate some one else's style.

My suggestion would be to introduce a theme though, such as "dungeon treasure" or "modern supermarket" or "overland trees" to both give people ideas and constrain it somewhat without being to limiting.

And I don't think splitting it into vector and raster symbols is a good idea. You're already cutting deep into the possible participants when you go from maps to symbols, so splitting even more isn't wise IMHO.

A symbol challenge could be a fun activity. I'll have to bow out myself though, while I can draw a decent CC3+ map from existing resources, creating my own symbols is far beyond me. I need those stronger in the art to do that for me.

A batch of great maps from @Quenten . This includes his contest entry, which means all contest maps are now in the atlas. I've also updated the contest page on the atlas site, and handed out the forum badges to the contest winners, so everything should be up to date.

As far as I know, the only thing currently in my backlog is a set of maps from @Wyvern . Everything else is either processed and added to the atlas, or I have gotten back to you requesting some kind of correction or information from you. So, if you are NOT Wyvern, but still miss me adding something you've sent me, please notify me immediately, as that means I've overlooked something. People send me maps multiple ways, as attachments to forum posts both in this common thread and in individual threads, as email and as forum PM's, so it isn't always easy keeping track of everything. I do always post in the forum when adding new maps, either in this thread, or in the WIP thread for that map, so if you haven't noticed me posting about adding your map, it might be wise to check the atlas.

Anyway, here's Quenten's new maps

Considering this is a generic underwater style, and not made for a specific setting, I think it is safe to ignore things like breathing, just assume that any DM who is using an underwater style have a way in the system they are using to handle that issue.