Just a really short post due to time constraints, but a necessary one. I've realized that in these posts (The first draft and the eventual ASCE journal entry) on the inward or outward force (sociofugal vs sociopetal) exerted on the real estate market (human emotion: want and need) by infrastructure lacked a foundation. Why was I talking about networks? And why was the simple mathematical exercise based on intersections within a set proximity?
The answer is something that I've never fully expounded or articulated, but it has been the foundation of many of my various studies over time. For example, see this post on Intersection Density and the relationship between lack thereof and Disinvestment and Decay. Or this one, where I gave different types of intersections, variable values based on the degree of convergence, or how many directions were merging at one place.
The reason is that the singular intersection is the basic building block of a city. Not a person, not a building, not a city block or a parcel of property. I've compared the city to both the internet and to a brain before and it is the intersection that provides the synapse. It is the spark of energy where to singular elements come together to create something greater than the sum of their parts, opportunity.
Intersections can be the connection between many things, for example skills and labor, or agricultural produce from fertile soil to markets, but to understand this we have to think about it at its very simplest, the crossing of two roads (which tend to be located between those things I mentioned at the beginning of the sentence, which in turn were located based on the intersection of various other needs and/or elements along Maslow's Pyramid).
The singular road is established between two points already pre-determined. However, there is no locational aspect along the road between those two points. Very little differentiates anything along those lines, assuming the geography is consistent throughout. For example, every point along the line would have a value of 1. It is along a presumably used route.
Only when a perpendicular road crosses, does that change the spectrum. While the remainder of the road remains a 1 at all points, the intersection might value up to a 2. And that it creates four parcels at each corner, that might create each of those parcels as a 2. Value goes up, there is more opportunity through more energy that passing traffic (of whatever form) provides. Because the value goes up, potential for increased density goes up to meet that value. Supply (of space) meets Demand (of opportunity).
It is that increased increment in connectivity which yields increased density. You can't just make density happen if the demand isn't there (which is the how and the why we subsidize so many projects to "inject" density. Unfortunately, without increasing demand through interconnectivity, we have no guarantee the "supply" of a new building will ever fill up without more subsidies such as deflated rents). This is where density comes from, not some complex financial equation as some supposed "experts" on density will say. The complex financials are necessitated only as a substitution for truly demand-driven density.
In modern terms, somebody might see the opportunity and add a gas station and quick mart at one of the corners (a modern day trading post?). That new business would need employees and employees have to live somewhere. Housing is built. Those residents have needs such as schools and recreation as well as other services, which can then be met. Provided the geography is amenable and there is enough traffic generated from the initial crossroads, this is a process that begins to create its own inertia until some form of carrying capacity is met (and then typically some form of technology expands that capacity if demand exists).
As the place grows the addition of intersections is necessary to ensure choice of route, flexibility, while the density of intersections is critical in 1) disciplining development patterns to engage the "conduits," thus tame those conduits so that they movement itself doesn't become pernicious to the value of the place, and 2) to maximize the percentage of site square footage that is the most valuable, ie frontage (see these two posts for the exercise: 1 and 2).
But underneath it all, every city starts with an intersection and expands by intersections, be they abstract or literal. With the size and proportion roughly of "private usable space" with public "conduit," ensures desirability through opportunity which makes for durable, sociopetal, demand-driven places.