It's diameter is about 100,000 light years. The Milky Way is thought to be an Sb or Sc in terms of the way Hubble catogorized Spiral Galaxies. This means that the Milky Way has an average to small sized central bulge and arms that are wound rather loosely around the center. The Milky Way Galaxy is within what is known as the Local Cluster. All Galaxies are within clusters, that is groups of Galaxies.
Some clusters are richer or poorer then others.
This is determined by the number of Galaxies in a cluster. Below is a picture of the Milky Way. Not the Galaxy but the stream of dust and gas that we can see from Earth. Below is a picture of what the Milky Way Galaxy might look like. Note the way in which the arms are wrapped around this Galaxy and the size of its bulge.