Space is one of those “we know it when we see it” sorts of things. That is not satisfying, though, if we would like, for example, to know which of two spaces is the larger. What criterion would we use to make such a determination?
Our goal is to refine our understanding of uninterrupted space. An immediate question, then, is what interrupts1 space? In most cases, this would be human constructions (roads, buildings, mines, etc.), but the concept can equally well apply in quite different settings, where other kinds of interruptions are appropriate to that situation. For example, to someone interested in the uninterrupted space of a lake, the shoreline and islands are appropriate interruptions. We are generally interested, however, in land rather than water situations.
SpacePreservation.org advocates using a “freedom to move about” concept to measure space—freedom of movement being conceptually equivalent to freedom from interruptions of movement. Here is one statement of the concept:
Space = Freedom to Move About
If you were dropped into a space (i.e., somewhere not on a road or other human construction) at a random point, and you then moved in a straight line to the nearest human construction, what would be the length of your uninterrupted movement? Then, if you did this experiment starting at many different points in the space, what would be the average length of uninterrupted movement? The greater this average distance, the greater the freedom of movement within the space.
A configuration of roads (black) with distance-to-nearest-road arrows (blue) at selected points.
Click or tap image to enlarge.
In the adjacent illustration, black lines represent roads and blue arrows extend from selected points (the tails of the arrows) to the nearest point on a road. There are no interruptions in this space other than roads. The length of each arrow is a measure of the minimum freedom of movement starting at the arrow’s tail. Starting from each of the arrow tails, uninterrupted movement is possible in all directions out to the distance of the arrow length. There is a circle centered on each arrow’s tail, with radius equal to the arrow’s length, that is free of obstructions.
An unambiguous metric
Earth is neither bare nor flat, so raw horizontal distance is not an accurate measure of freedom of movement. It is, however, unambiguous. SpacePreservation.org advocates the use of simple, unambiguous, geometric concepts and measurements of space — and therefore recommends space measurements based on straight-line, horizontal distance.Topography, land cover, and other complexities introduce estimates; for example, how fast might one move through a forest or a swamp, or across a gully—and should these different difficulties of movement count in a space metric? Estimates of movement under variable conditions are ambiguous and arguable. SpacePreservation.org advocates the use of simple, unambiguous, geometric concepts and measurements of space—and therefore recommends space measurements based on straight-line, horizontal distance.
Unobstructed views are conceptually equivalent to freedom of movement on a flat, bare earth. In this notion, if you were dropped into a tract and it could be magically flattened and stripped of view-blocking vegetation—thus removing natural obstructions of your view—then what is the nearest thing, now necessarily human built, that obstructs your view? A tract has more space if it has larger average unobstructed (uninterrupted) views.
In practice, the idea of freedom of movement can be turned into a measurement that can be calculated on a computer from digital maps. If you spend any time on this web site, you will see that we are strong advocates of map based measurement of space.
|Measuring Space I
Illustrates conceptual problems with using area as a measure of space and loss of space.
|Measuring Space II
Introduces the space volume measurement that combines area and distance.
|Some Space Terms
What is open space? How about protected space? Here are our uses of various space terms.
|Back to: Open Space—Our Vanishing Resource
Overview of the forces behind space loss.
|Play with it—Space in your home
Ready for some fun? Learn about space by moving your furniture.
1 Later, when we present specific measurement methods (see Measuring Space II), we refer to space interruptions more succinctly as “foils”, because these features are the things against which space is measured. Space is measured against its foils.