Both of the above meteorological parameters fail to meet the need for a true and universal climatic description. Vegetation, however, offers a useful guide, particularly in special cases, such as the selva, or equatorial rain-forest belt, with hot tropical rain much of the year; the savanna, with warm, strong seasonality; and the tundra, with cold, strong seasonality. It is a particularly helpful system for a person who wants to know the nature of an area and what it is like to live there. Because temperature relates to precipitation in terms of potential evaporation, a classification based on the latter two provides an excellent guide, with four fundamental divisions: hot-dry (arid), cold-dry (polar or glacial), hot-wet (selva), and moderate-warm to cool-humid (temperate).