A greenfield development site is one that has not been built upon previously. It is often agricultural land but it can be undeveloped land in a city or rural location. Greenfield sites offer developers a blank canvas and tend to be cheaper to develop versus brownfield sites, as nothing has been built on them previously. However, greenfield sites maybe subject to legal and planning constraints and may require associated infrastructure investment (for example providing new roads and utility connections).
A brownfield development site is one that has been used before. Frequently these are disused or derelict land that have been used previously for industrial and commercial purposes but have since become abandoned. Brownfield sites often require expensive clean up operations, for example, knocking down existing buildings or decontaminating land due to its previous use, and so may be cheaper to purchase as a result. However, such sites often suffer from restricted access as they tend to be surrounded by other buildings that are still in use, but may benefit from access to infrastructure that is more likely to be in place versus a greenfield development.