Edges in landscape are everywhere,.. overly common, yet at times incidental. Each landscape space offers different programming, functions or physical characteristics. At the boundary of each space is an edge...these are the transitional spaces from one landscape or space to the next (i.e.: the entrance into a city park, the bridge to a connecting highway, the riparian zone linking biota).
Landscape edges are transitional linear places where one space or landscape becomes part of another. Often neglected in design, edges are considered primary structural components of landscapes because of their integration and social functions.1 They offer not only physical change, but emotional and psychological transitions as well.
Edges can be where the picturesque meets the pastoral, built meets unbuilt, city meets country. Woodlands edges, wetlands, beach fronts are considered strong edges, and can also be referred to as "ecotones" - physical transition zones between two ecological systems. These edges and corridors strongly influence landscape biodiversity, and in many situations when designing them -- the suggestion is that the "lightest hand" is the hand that designs best.
Some edges are purely physical (a building meeting terra firma) while others are visual and symbolic (earth or sea meeting sky). Some edges are abrupt while others are smoothly drawn out and richly complex (i.e.: a woodland edge, a waterfront).
As an urban dweller, I am most cognizant of the juxtaposition between two systems that are forced to co-exist within a city- the built form and the natural form. John Motloch, speaks of the "dynamic nature of natural systems versus the static nature of architecture." Natural systems are point-in-time expressions of ongoing environmental processes: site and living organisms continually experience change. Conversely, architecture consists of relatively static elements. Architecture changes little over time. Buildings do change expression - from transparent, to reflective, to opaque - from day to night. Plant materials, on the other hand are living organisms and mature over time. Even senility in the landscape can be one of the most sensual aspects of landscape design."2
Within these edges are "thresholds"*, uniquely centered entities within the linear form of an edge. The Collins English Dictionary defines threshold as “the starting point of an experience, event or venture; a psychological point at which something would happen or would cease to happen, or stimuli would take effect.”
These thresholds provide tremendous opportunities for designers to create gateways within them and experiential transitions within that journey. "A gateway denotes a threshold, a place of passage, a garden gate that opens and closes, a bridge point of entry into a city, a harbor of access to some hinterland. A gateway can have many forms, a literal gate, an avenue of trees, an entrance into a building... yet they all have the same function --to mark the point where a path crosses a boundary and help maintain the boundary. All of them are 'things' - not merely holes or gaps, but solid entities. In every case, the crucial feeling this solid thing must create is the feeling of transition."3
St. Louis on the edge of the Mississippi River is known as the "Gateway to the West"
Edges are also topographic. Perhaps simple and smooth with gradients and rhythmic sequences or textural and rugged, spurred, ditched and jagged, natural or built with sub-spaces or steps. Of particular note on a grand scale is the Isthmus of Panama - a narrow strip of land where geological tectonic plates meet, the landscape changes often and dramatically. It became a major inspiration for Frederick Law Olmsted in developing an aesthetic for public parks as he crossed it in 1863.
1. Form and Fabric in Landscape Architecture; Catherine Dee.
2. Introduction to Landscape Design; John Motloch
3. A Pattern Language: Alexander/Ishikawa/Silverstein.