Released on September 1, 2016, Possum is an algorithm update affecting local search results on Google. Long story short, Possum diversifies local results by filtering clusters of similar businesses located very close to each other so that only the best listings in each cluster are shown to the user.
Possum also had an impact on the local rankings of businesses with addresses just outside the demarcated borders of municipalities recognized by Google. Prior to Possum, these businesses would struggle significantly to earn local rankings. After Possum, earning local rankings became more of an even playing field.