They will be smaller and will consist of isolated solar systems, probably in the galactic halo. The planets should be compatible for terraforming and would offer good conditions for settlers. In those areas, there must not be risks or a nova, supernova or that Red giants might explode. They consist of safe solar systems, mostly stable M - type stars, K - type stars and G - type stars.
The galaxy can be divided into different areas: Once we know the real position of existing stars and we have an idea about the solar systems that inhabit the galaxy, we can focus on the next stage of the project. All data must be gathered together and fast. Given the huge size of a galaxy, the process will require a huge number of ships. During the research phase, many automatic, fast moving spaceships have to travel throughout the galaxy, to carefully map its real structure. Also, new stars have formed in places we don't quite know. Since light needs sometimes billions of years to reach us, majority of distant O - type stars and B - type stars no longer exist. As light travels with a fixed speed, all stars you see are actually older.
One major problem is that the real shape and structure of a galaxy is not the one you see. However, if a civilization expands slowly, it will annex solar systems one by one, then will expand to larger areas of space. For a fast colonization, the research phase will be done to the entire galaxy.