A few years ago, a friend gave me a little article he wrote (not published, so I can't send it to you) that he entitled, "How to Think about Leadership." It was an overview, a set of categories actually, of the various ways that people have written about leadership. I've long since lost it, but it was a helpful tool when evaluating authors who write about leadership.
As I read for my PhD I have noticed that there are also categories of missiology. These might help to understand an author's perspective and how the text is intended to be used. There are four broad categories, with a myriad of smaller subcategories underneath them. FYI, my working definition of missiology is "The study of God's movement in time and place."
The first of these three categories is observational. Historical research and analysis is applied to the question of how Christian movements have formed and grown. In this school of thought, understanding movements is essentially a study of Christian history. Getting a comprehensive view of Christian history is a challenging task. There are, of course, the standard problems in recreating any historical account and this is the challenge of observational missiology. Autobiographies, historical accounts, reports from the field, and a great deal of research is a part of this branch of missiology. This category seeks to answer the question of "What happened or is happening?"
Another category is applied missiology. These authors are most concerned with how Christians should carry on their work in order to create or support Christian movements. Their work is often filled with prescriptions and recommendations for how church and mission is to be conducted. Often, there is a sociological root to the views expressed by these missiologists. How-to courses and manuals intended for churches or missionaries, prescriptions on church planting strategies, community development paradigms, various "special interest" missiologies (i.e., children at risk, environmentalism) would fall under this broad category. Applied missiology answers the question, "How should we go about our work?"
There is, of course, much theology embedded in the first two categories. However, some missiologists focus more exclusively on the theological basis of mission. Systematic theology, Biblical theology, and other theological pursuits are similar in nature but have distinct emphases that are different from missiology. Examples of this sort of theological missiology includes NT Wright's, "Jesus and the People of God," Christopher Wright's, "The Mission of God," and a lot of Newbiggen material. The overarching question that theological missiology seeks to answer is "What is mission?"
Local missiology utilizes any of the previous three categories but is tied to an underlying worldview, culture, or region. This might be the author's own perspective or it might be the authors reflection on another culture. The emergent church authors, for example, are distinctly concerned with postmodern, Western, missiology. It does not translate well to the plains of Africa, where a much different missiology has developed. Because we are all trapped by our culture, all missiology might be considered local at some level. However, this category is reserved for those authors that are writing about missiology in a specific context. It answers the questions, "What does this cultural context say about mission?"
The best missiology happens when these categories are fused together. They are not independent of each other, but work together to form a whole. Unfortunately, this is often not the case.