I tried this, but I can't seem to find what you're suggesting. When I click "More" there is no "other" option. My options are "Assign Tags," "Store Page & Reviews," "Support," "GOG Downloader Links," "Forum," and "Hide Game." I checked the "GOG Downloader Links" tab, but didn't see anything labeled editor.
Just because of you I installed it.....
IN the german version ( and I assume english the same) you can find the map editor in the startmenu under tools......
sirblockwood might have phrased it a bit badly, making you assume that he was talking about the GOG-page.
And just to be clear and avoid confusion ;)
startmenu -> programs -> Anno 1602 -> tools ->>>>> map editor <<<< ;)
(Yes a wee bit of teasing ;) )
And to be honest, I assumed the same as you hence I installed it :D (just for you :P ;) )