material=aluminum and surface=* was the advice from someone on the community forum.  They said that while the ramp was aluminum the surface could be anything.  In this case its a non-slip rubber mat.  I suppose that tag could be removed.  I wrote about the non-slip rubber mat in the description and as someone on the US Slack said gangway will confuse them, I'll just remove that tag.  Bottom line.  I have to go there again anyway.