Thank you for your idea about the hiding the selected bookmark categories in map! We'll keep your suggestion in mind.
How it works now:
To hide a particular bookmark from the map, just tap once on the item name in My Collections list. It turns the font colour from black to gray; i.e. black – for visible, gray – for hidden bookmarks. Tap it again to show the bookmark on map.
Read more about bookmarks: http://galileo-app.com/help.html#bookmarks