There's a fundamental misconception about the way cities should be built that, when enacted, deprives urbanism of much of its richness. If you zoom way out on a city, like this image of Philadelphia, it can look like a fried egg, with a big "egg yolk" of tall buildings at the urban core thinning out to an "egg white" of urbanism that is only a story or two tall at the edges. At this distant view, it looks like a fairly smooth transition, and in fact, this is largely the way cities have been zoned for the past several decades: large swaths of high density surrounded by larger medium density zones giving way to even larger lower density zones. Great urbanism, on the other hand, is much more fine-grained than that, so that wherever you are in a traditional city, there's urbanism just around the corner or down the street that's decidedly different from what you're seeing at any given moment.
Coding entire neighborhoods to a single context like we've done in recent decades is a bad idea on several counts. For starters, it's a prescription for boredom, whether that context is equal to Main Street or a suburban residential street. If that context rolls on for neighborhood after neighborhood like it does in the subdivisions of sprawl, then this means that you're unlikely to walk anywhere that doesn't look like where you live.
Why is this a problem? Because if where you live is primarily residential context (in other words, if you're not living in an apartment over Main Street,) then it means that you're unlikely to be able to walk to all your daily needs. This forces you back into the old sprawl burden of having to drive everywhere… even if the streets and buildings are generally well-designed. In other words, too much of a good thing is actually a bad thing.
The Increment of Planning
So if the neighborhood isn't the right increment of planning, then what is? The block? No, the block is also too large. Some blocks might all be coded to the same context, particularly if it's the general neighborhood context, But most blocks in sustainable places are likely to contain more than one context zone. It turns out that the fundamental increment of sustainable planning is actually the lot.
Some planners go nuts when you say that, because they're accustomed to seeing a nice, neat Euclidean zoning map of an entire city whereas zoning with individual lots as the basic increment gets so fine-grained that you can't even see all the breaks when looking at an entire city map… they're just too small unless it's a mammoth map. This doesn't mean that each lot is randomly zoned (planners call that "spot zoning".) Rather, it means that when you change contexts, you do so most often at property lines rather than at streets or at the edges of neighborhoods.
Context Zone Breaks
Here are four good rules of thumb for breaks between different context zones:
1. Change from one context zone to another in the middle of the block, not at a street. You usually want the front of a building to be looking across the street to a building of similar context. So the end of a Main Street, for example, should not be at a cross street, but one (or maybe two) lots beyond that cross street.
2. Make context breaks most frequently "with the grain" of the block. In other words, the break occurs between back lot lines, or at the alley or rear lane in the middle of the block.
3. Breaks can also be "across the grain" of the block, like this picture. Here, the break occurs at the side lot lines.
Here's the town of Pienza, Italy, which I've used several times to illustrate various ideas on this blog. The old city, which is the compact part, is only 11 acres. The two images which follow overlay the context zones of the Transect, or T-Zones, as they are known to Transect experts.
Two Important Points on Time
1. Pienza was built over a period of roughly two thousand years.
2. The Transect wasn't even invented as a planning device until centuries after most of Pienza was built.
Pienza's Transect, and that of countless other places built sustainably over the millennia derived not from some grand plan of city planners. Indeed, most such towns had no planners at all. They were merely built by the townspeople using good rules of thumb. So how did their Transects come about? They were common-sense responses to some very basic needs:
1. People need to be able to walk to work, if they're not working at home. This means that home and work need to be near each other.
2. People need to be able to walk to their daily necessities, like groceries and such. But if you scatter shops all over the neighborhood, that makes it more of a chore to shop. So it makes sense to have most of the shops relatively close together, like along a High Street or a Main Street.
3. People need to be able to walk to their civic buildings, so they can participate in the life of the town.
4. Towns shouldn't spread too far because streets and other infrastructure are expensive, so the Sub-Urban parts of town, because the are least compact, should be fairly small so as to not waste infrastructure. As a matter of fact, most of Pienza's Sub-Urban parts were built in the last century or so, after the advent of automobiles and cheaper streets. You can see that the Sub-Urban parts in the old city are really small.
5. Compact towns and neighborhoods are more secure not only because you have a smaller perimeter, but also because more compact urbanism can put more eyes on the street.
6. Towns (and even cities) need to be surrounded by the countryside that feeds them because if you can't eat there, you can't live there.
The Transect and the Original Green
Sounds familiar? If you've been to this site before, I'm sure it does. These simple needs that led to countless sustainable places built over the centuries are the needs for Nourishable Places, Accessible Places, Serviceable Places, and Securable Places. In other words, the conditions that created the Transect around the world are the same conditions that the Original Green works to organize, just in a different way. You might say that the Transect and the Original Green are really just two different views of the same thing: how to build sustainable places, which are places that you can keep going in a healthy way, long into an uncertain future. Here's where people get confused:
There are certain characteristics of built environments (described above) that have been sustained in a healthy way for centuries that we can observe again and again in place after place around the world. Without these characteristics, humans have yet to build places that are truly sustainably... in most cases, places without these characteristics are hideously unsustainable, with sprawl as Exhibit #1. So it is fair, IMO, to consider these characteristics "essential."
A century ago, the ecological transect was invented as a management tool for the built environment. Less than twenty years ago, it became clear that this tool could be extended into the built environment in a way that explains those essential characteristics of sustainable places, and that also can form a guide to building new places that are also sustainable. This is known as the rural-urban Transect. The Original Green is even newer than that: Although its roots go back to the day after Thanksgiving, 1980, it was not formally assembled as an idea until less than a decade ago.
Ancient Things That Work and New Tools
The problem comes when the distinction isn't made between old and proven ideas and new tools for implementing those ideas, either by those who promote the new tools like the Transect or the Original Green, or by those who respond to what they say. Both the Transect and the Original Green are idea that are clearly new and open to refinement… matter of fact, they are regularly being refined. But the essential characteristics of built environments that they attempt to make sense of have a successful track record stretching back a few thousand years, and assailing those characteristics, especially when there has never been a successful alternative but many hideous failures, doesn't seem to be a profitable way of spending time.
Other Sprawl Recovery posts on the Original Green Blog: