Since the beginning, CalTopo has had the ability to make maps publicly visible, i.e. someone can find the map without knowing its URL. However all this did was add the map to an obscure page that few visited other than Google.
Today that changes with the introduction of the shared maps layer. It's available as an overlay checkbox, along with a layer for your own maps that's visible when you sign in:
At wider zooms, each shared map is shown as a simple bounding box and center marker. This can get a little confusing - some additional UI love may be necessary - but mousing over highlights the box and center mark. Clicking brings up an info window with a link to that map:
Zoom in a little further and individual features get displayed:
Mouse over a feature and everything from the source map will get highlighted, giving you an idea of what that map covers. Clicking gives you the feature's name and comments, if any, and another link back to the source map.
So how do you share your maps with other CalTopo users? When saving a new map, just choose "publicly visible" under the "Share Your Map" section of the save dialog. Go ahead and fill in some details in the "Tell Us About Your Map" section as well.
For maps you already have, start by clicking on your account name at the top of of the left bar.
Then go ahead and and set the sharing dropdown to "Publicly Visible" for each map you want to share.
This might be a good opportunity to visit the "Your Account" tab in the same dialog and change how your account is displayed to other users. I'm also putting a messaging system in place so that other CalTopo users can ask questions about your maps. If you don't want them to be able to contact you, uncheck that box.
There are only around 500 maps currently shared on CalTopo. As that number grows I may need to change some of the implementation details to improve performance or reduce information density, but I think the basic approach is here to stay. I'm pretty excited about it - I've already discovered a few maps that I wish I'd known about sooner.