What is the disicpline of Geography?
At its most fundamental Geography is concerned with the spatial distribution and patterns of practically anything, it is a spatial science, and so although the discipline is one of the most wide ranging, and acts as a bridge between the physical (natural) and social sciences, what we see is discipline of which its relevance is constantly being renewed. For example, turn of the century medical geography was concerned with the spatial distribution of diseases such as Cholera, and we see techniques such as disease mapping and spatial epidemiology (study of spread) used. Today we have the New Geography of Health, focusing on the spatial distribution of health care facilities and healthcare consumption such as the mapping of Gyms, although the subject has changed so much this concern with spatial sensitivity places geographers in a good position to deal with increasingly complex situations.
To say a little about the disciplines creation and future. Geography really arose as a important subject in the mid to late 19th Century and a whole branch of literature focus's on the self critique of the discipline. It highlights that the need for geography was cemented in imperialism and the colonial project. The British empire needed knowledge and understanding of different areas of the world in which to justify colonialism, as well as good mapping techniques. There is particularly good writing on how the British Empire used the subject at the time steeped in the environmental determinism (Darwinism) and survival of the fittest as well as the drawing of maps ignoring indigenous settlements, i.e. depicting areas as empty and in need of colonizing, such as those drawn of Australia around this time.
So what we see is that geography was originally focused with cartography (the drawing of maps)as well as regional geography, the understanding of a particular region on the planet (usually a country) and to understand the physical and human characteristics, that is to say they are intertwined.
Since then we have seen the decline of regional geography, generally out of irrelevance i.e. you can not deal with one area without an understanding of another, e.g. you can't explain the closure of factories in one part of the world without understanding the rise in cheap labor in another. After regional geography, something that the majority of us learnt in school, we find new forms of geography based in globalization (cultural/historical/economic geography), based in power relations (geopolitics), river flow (fluvial processes) etc. That is to say that geography has become a subject of sub disciplines, all distinctly different.
Today geographers are concerned with contemporary issues such as abrupt climate change, globalization and how we can consider this a new form of imperialism, predicting and preventing disease e.g. obesity and cancer through smoking, and many other research areas, therefore geography is very much aligned with other subjects.