Erith is in Kent - the "Garden of England" - I can only assume Erith is the outside toilet because it is a shit house.
Would it make sense to say in some selected context that people from Slade Green are underepresented in that context? If you enlarged it a bit, would Erith or Crayford or even north-west Kent make sense as things which could be underepresented? I suspect not, because there are thousands of Slade Greens in the United Kingdom, thousands of places with nothing going for them and no special claim to be represented somewhere else. If someone from Slade Green became a Hollywood film actor ( Jade Anouka might) the fortuitous fact of coming from Slade Green would be of no relevance. If Jade Anouka got a part, no one would be asking the question, Are Slade Green actors under-represented (or over-represented) in Hollywood movies?