Sure, we all know how to do that by know, right?
Funny thing is, all the blog entries I've seen like the ones here and here, end up creating a new map, usually situated in the root of your assembly (or event worse, create temporary orchestrations to do that). In order to move it to another folder in your project you'll have to edit the XML contained inside the map since it contains relative paths to the schemas mapped (and watch out for those namespaces).
Here's an easier way to do it :
- Create your empty map exactly where you want it.
- Add a transforms shape and open up the properties.
- Instead of choosing new map, choose existing map.
- Select your newly created (empty) map.
The BizTalk Editor will modify the map to take the new message types - multiple if you selected them.