Constructing a "map" of your chosen topic can be an effective strategy for finding a specific focus for your research
This example provides a demonstration of this strategy, using the issue of Public Transportation.
The example above provides a "map" of issues relevant to the overall topic. You can then use this to navigate around your chosen topic and locate a definite focus. The map below charts the possibility of researching the environmental benefits of using commuter rail systems in cities and regions.
Public Transportation in the United States