As noted in Chapter 12, a professional, polished dissertation is one that is well referenced. You should always take time to get your referencing right. Referencing is vital to ensure you have given due credit to the work of others whose ideas you may have used. The Harvard system is the most frequently used form of referencing for Geography students. That said, for some historical projects, footnote referencing (in the Oxford or Chicago style) might be preferred.
There are various guides to referencing available online. You can find a link here which provides a comprehensive guide to Harvard referencing, and Footnote referencing. These are specific to the institutions they relate to, but they also provide good general information. Be sure to refer to your own institutional guidelines too (see Task 1.1 in Chapter 1).