What constitutes a park?

What is a park? What are the necessary minimum conditions for a park? Which kind of functions it is about to serve?

According to a simplification by Cranz, there are three basic visions of parks, their functions and their onthology. A naive vision of park implies that they are mere plots of (unused) and thus preserved land, being manifestations of democracy as they are free for anyone. Parks can be considered works of art, aesthetic objects. Then, parks can be containers of moral and social (reformist) ideals, as the case was with the idealist ideology behind the Olmsted Central Park in New York. (Cranz 1982, 253.)

According to Jacobs, the four elements essential to successful public parks are those of intricacy, centering, sun and enclosure. By intricacy Jacobs means the principle of multiple use: parks should be used by different persons, for different purposes and at different times. Even the same user might use the park for different purposes at different times. By centering Jacobs means that there usually is a focus of actions and encounters in parks, perhaps a
crossroads, a pausing point, a climax. In neighbourhood parks these centres may be stage settings for activities for and encounters of people, according to Jacobs. While the sunlight is essential for parks if conceived as public open spaces, then a city forest, such as the Central Park of Helsinki provides the shade, although the altering of sun and shade are frequent elements in any park. Finally, the parks represent an open space between the buildings, but
without any buildings they would be indefinite. The buildings enclose the park, if they are not too high and provide too much shade, attaching the park to the city both functionally and locationally. (Jacobs 1961, 103-106.)