ABSTRACT
This chapter defines what the term migration stands for in theory, while emphasising that the practical definition adopted is often highly dependent upon the available data. Additionally, a number of terms that are commonly used in relation to migration are defined. Some influential sources of migration data are outlined and, although many of these sources are common to different countries, British migration sources are focused upon to show how the implied definition of migration and the adequacy of the different data sets varies considerably. The chapter also explains how migration is actually measured, beginning with the most simple descriptive methods and leading on to more advanced analytical methods that help us to explain the migration process. Although most of the methods described are quantitative, the importance of qualitative methods in migration research is illustrated with examples of qualitative methodologies. While certain techniques have become fashionable at certain periods, often matching the changing philosophical direction that geography has taken (Chapter 3), the relative strengths and weaknesses of the various methods need careful consideration. The choice of technique depends crucially upon the aims of the research project in hand.
