I think I figured this out - electoral districts are subject to change every two years i.e. gerrymandering - while enumeration districts are every ten years using census data - may not be correct but makes sense to me

I think election districts change every ten years. That is because after the census taken every ten years, these districts are supposed to be redrawn to reflect the population changes.

Sorry left this part out. Gerrymandering is supposed to be illegal. That is shortening, elongating and twisting the boundaries of a district for political purposes.