A valley is the generic term that consists of Flats, Forests, Lakes, Swamps, Hills, Deserts, and Grasslands. So yes, a flat is a valley.

- A flat is an area of land that you may attack and if successful, take for your own. The purpose of a flat is to build more cities. When somebody constructs a city, and abandons it, the barbarian city level is that of the flat when he/she conquered it.

- A forest is an area of land which has many trees and shrubbery. You may attack and if successful, takes for your own. Forests are extremely useful, because they increase lumber production. The higher level the forest is, the higher percent increase you will receive upon conquering.

- A lake is an area of land that you may attack and if successful, take for your own. Lakes are used to increase food production, and are a higher percent increase than grasslands. A higher level of the lake means a higher increase in food production.

- A swamp is an area of land that you may attack and if successful, take for your own. Swamps are also used to increase food production. A higher level swamp results in a higher increase in food production.

- A hill is an area of land that you may attack and if successful, take for your own. Hills are the only valley that is used to increase iron production. A higher level hill means a higher increase in iron production.

- A desert is an area of land that you may attack and if successful, take for your own. Deserts are also the only valley used to increase stone production. A higher level desert means a higher increase in stone production.

- A grassland is an area of land that you may attack and if successful, take for your own. Grasslands are used to increase food production. A higher level grassland results in a higher increase in food production.

Remember, your valleys can be re-conquered by other players, so be sure to defend them well.