L +/- Gx = $ = p
WTF does that mean, amirite?
Derived from the awareness that over time, places, though always in somewhat constant state of flux if there are no other infrastructural changes, will reach an equilibrium where highest and best use is responsive to the surrounding infrastructure. In other words, density equals what the infrastructure and interconnectedness of a site allows.
Given that for development to be predictably successful, density has to be proportional to desirability. I like the statement Density = Desirability. Because it is 1) responsive to demand processes, but also 2) if places get too dense, they can become undesirable themselves. In other words there are diminishing returns if there is an imbalance of building height to public space, or out of proportion building space to public space or vice versa for the agoraphobic.
Somebody responded on twitter that density rarely = desirability. This is partly true and partly a strawman. As I said, at any one point in time an area is trying to find its equilibrium. A snapshot doesn't capture the trending direction of a property nor the infrastructural "improvements" that may be actual improvements to the network interconnectivity or may not be improvements at all. Again, lots of moving parts. The key is determining where a site, area, neighborhood, or city are at any one given point in time, establishing the goals, and following through with the infrastructural network interventions to achieve those goals.
What the equation above symbolizes is the following:
Local Connectivity Plus or Minus Global Connectivity (to a variable exponent degree) Equals Value of a site, which then in turn Equals Density.
Value is driven by connectivity because connectivity is what is the release valve of demand.
If a place is locally connected but not globally connected it will be of low value and low density.
If a place is globally connected by not locally, it will lack durability, resilience. The infrastructure and auxiliary impacts of global movement is generally undesirable to be around. Would you like to live next to a highway or airport runway? The "other side of the tracks?"
This is why Global connectivity often detracts from Local and therefore has a negative overall value on place. If you want to maximize value, a place has to be both globally and locally connected, but sure that one doesn't disrupt the other. This is why subways are good because they're tangential to local networks at street level, though very expensive. It is the subway systems in major cities that allow for great density but little to no other global interconnectivity, such as highways through the fabric. Even if you bury the highways, they have to exit somewhere. The exiting infrastructure and parking is corrosive to local networks the way vertical circulation from subways are not.
Global connectivity is the amplifier of value for better or (and more often) for worse. Like too much density, too much global connectivity detracts from overall value, particularly over time. You want to maximize the two networks, integrate them, make them complement each other, and know what is appropriate where.
Often we try to put too much in places that aren't ready for it too soon. The, "build it they will come" mantra. And this is why all-at-once mega-developments or mega-cities fail. They tried to skip the necessary feedback loops where integration begets accommodation begets decoration, then more integration and so on and so on. This is the way cities evolved organically from time in memoriam. Developers, investors, and planners alike should follow this formula...that is, if they're actually concerned about long-term, resilient, lasting, and increasing value.