The methods for analysing community composition or similar kinds of multivariate ecological data are usually divided into gradient analysis and classification. The term gradient analysis is used here in a broad sense, for any method attempting to relate community composition to the (measured or hypothetical) environmental gradients.

Traditionally, the classification methods, when used in plant community ecology, were connected with the discontinuum approach (or vegetation unit approach) or sometimes even with the Clementsian superorganismal approach, whereas the methods of gradient analysis were connected with the continuum concept or with the Gleasonian individualistic concept of communities (Whittaker 1975). While this might reflect the history of the methods, this distinction is no longer valid. The methods are complementary and their choice depends mainly on the purpose of a study.

For example, in vegetation mapping some classification is usually needed. Even if there are no distinct boundaries between adjacent vegetation types, we have to cut the continuum and create distinct vegetation units for mapping purposes. Ordination methods can help find repeatable vegetation patterns and discontinuities in species composition, and show any transitional types, etc. These methods are now accepted even in phytosociology. Also, the methods are no longer restricted to plant community ecology. They became widespread in most studies of ecological communities with major emphasis on species composition and its relationship with the underlying factors, and they have found their way also into research fields unrelated to natural sciences (archaeology, social sciences). In fact, it seems to us that the advanced applications of gradient analysis are nowadays found outside the vegetation sciences and the methods become more frequently used in freshwater and marine studies.