Back to the Real World
The synthetic approach to central place
geometry, in earlier chapters, has found application (by S. Arlinghaus
and others as noted) in the usual and the unusual. The articles below
have all appeared in Solstice and links to those articles are given
below (Solstice, itself, is a Pirelli INTERNETional Award Semi-Finalist
(top 80), 2001).
For the city to offer a fine quality of life to all its residents (taxpayers and others) there need to be mechanisms to create continuing economic development within the city. One way to do this is to increase the stock of housing and space for commercial and other establishments in support of that housing. This path is all the more attractive in light of enduring interests in reducing "sprawl" and in preserving open space in the more rural surrounding lands. In a city with few remaining empty buildable lots, this approach seems to offer few alternatives, the most obvious of which is to increase the density of dwelling units within the city. When density increases are proposed in established residential neighborhoods there is often loud and long public objection from residents of those neighborhoods. There may also be serious environmental considerations, as well. Few residents, however, seem to object to increasing density in the downtown: many who already live there moved in with an acceptance of taller buildings and those who do not live there often do not care about the idea of increasing density in the downtown. What people do seem to care about, however, is what an increase in downtown residential density may mean to the character, appearance, and feeling of the downtown. To some, an 18 story building is a visual blight on the skyline that provokes negative comment everytime it is viewed; yet, others note that they have become accustomed to it and view it as an old, familiar friend. Building height can be a source of substantial dispute.
The problem of where to locate tall buildings, with sensitivity to existing building types on adjacent and nearby lots, is a difficult one. In Ann Arbor, building height is currently limited by "floor area ratio" (FAR). The FAR is calculated as the ratio of floor area in a building divided by parcel area, times 100. If a given parcel has an FAR of 100 assigned to it, then a building footprint built lot line to lot line may have a height of 1 story. If a parcel has an FAR of 200 assigned to it, then a building footprint built lot line to lot line may have a height of 2 stories. Similarly, an FAR of 300, assigned to a parcel, yields a building of height 3 stories covering the entire parcel. Thus, on a parcel with an FAR of 300, one might, instead, build a building on half of the lot area but of height six stories, or on a third of the lot area but of height 9 stories. On the same parcel, a 30 story building could be built only if its footprint covered one-tenth of the land area of the parcel.
The FAR provides a height limit based on the size of foundation needed to support a tall building. It also offers subtle encouragement for preserving some amount of open space and visual variation in the region to which it applies. The drawback is that a tall building may get built with no regard to the broader context of how a new building will fit in with existing buildings on the surrounding parcels. A possible side effect of using FAR (alone) to limit height is that it might encourage parcel amalgamation by large developers, thereby driving out desired local small business owners.
The issue of creating greater height in the downtown is a complex one. In 2003, Mayor John Hieftje and the Ann Arbor City Council established, in conjunction with the Downtown Development Authority, DDA, (Susan Pollay, Executive Director) a Taskforce to study increasing residential land use in the downtown. Some of the materials studied by that group was created by the first author, in collaboration with others (Fred J. Beal, President Beal Construction, and Douglas S. Kelbaugh, Dean Taubman College of Architecture and Urban Planning, The University of Michigan). The material that follows highlights the use of concepts from this book that were used in that context. It, and associated materials were used in public hearings and by City Council in passing the recommendations of that Taskforce. A more complete story of the policy and 3D modeling aspects is available elsewhere (link to Arlinghaus, Beal, and Kelbaugh).
A Prime Parcel
Sieve.
The FAR is assigned by zoning type.
In the downtown, there are currently parcels assigned to each of 22 different
zoning categories (AG, C1, C1A, C1AR, C2A, C2AR, C2B, C2BR, C3, M1, M1A,
M2, O, P, PL, PUD, R1D, R2A, R2B, R4B, R4C, R4D). Roughly speaking,
any category beginning with C is a commercial category; M is for manufacturing;
R is for residential. The AG category is for agricultural zoning,
O is for office, P (except for PUD) is for Public Land (as for the University
of Michigan), and PUD is for Planned Unit Development.
Figure 6.1. Zoning animation of 22 zoning categories: AG, C1, C1A, C1AR, C2A, C2AR, C2B, C2BR, C3, M1, M1A, M2, O, P, PL, PUD, R1D, R2A, R2B, R4B, R4C, R4D. Zones enter the animation in alphabetical succession. Attached labels are added in the final frame. |
The casting out of parcelsWith an enumeration of all parcels in hand, groups of parcels will be removed in accordance with various ideas. The goal is to select targets of opportunity for taller projects. The mechanism for such selection is similar to the mechanism for the selection of prime numbers employed by Eratosthenes (link back to Eratosthenes's Sieve). In the case of the downtown, parcels meeting certain criteria are cast out from further consideration as prime parcels much as numbers meeting certain criteria (multiples of 2, multiples of 3, multiples of 5, and so forth) were cast out from further consideration as prime numbers. What remains, are "primes": prime numbers or prime parcels. These prime parcels will then be viewed as possible targets of opportunity. Local considerations of various sorts might then be superimposed on them, such as design standards, spacing of tall buildings, or whatever constraints are within the legal code of the city.
Figure 6.2. Zoning categories, DDA boundary, railline, floodway and floodplain. |
CASTING OUT:
Figure 6.3. All zoning categories other than C1A, C1AR, C2A, C2AR, C2BR zoning categories are cast out from further consideration. Those 5 zoning categories cover the lands represented in white (as in open for further consideration). The parcels assigned a color other than white have been removed from consideration. |
Figure 6.4. This map is identical to the map in Figure 6.3 with historic district parcels superimposed in red. The historic district designation further limits the targets of opportunity. |
Figure 6.5. Zoom in--the aerial replaces the white zone in Figures 6.3 and 6.4. The locations of existing buildings and surface parking lots become evident. |
The map in Figure 6.5 shows each parcel
from lot line to lot line. Building footprints were digitized from
aerials provided by the City. Associated databases gave estimates
of building height. Interactive
maps offered a constructive way to link a variety of two dimensional
sets of information (as in Maps 6.1, 6.2, and 6.3).
Designing
the Vertical City: the Use of Virtual Reality Models
Once the parcels that could serve as targets of opportunity for tall buildings were agreed upon by the Taskforce, the prime parcels, a series of several hundred virtual reality models were developed to visualize alternatives for the DDA. The reader interested in the detail of the planning process, local policy matters, and the mechanics involved in model construction are referred to the following materials in the references. The focus here is on the use of a concept identical to Erastosthenes prime number seive to sift out parcels elegible for further consideration, as above, and the subsequent application of virtual reality to visualize complex geometric situations, as in the case of Christaller nets, in order to facilitate scientific communication and eventual policy decisions by official municipal bodies.
The set of buildings that currently exist
within the DDA was used as a base on which to build alternative scenarios
of what might be done. Figure 6.6a shows a screen-capture of a virtual
reality model built by extruding building footprints according to height
records from the City of Ann Arbor Planning Department (Figure 6.6b is
the virtual reality model; try driving around in it).
Figure 6.6a. Downtown Ann Arbor buildings extruded from footprints digitized from aerial. Figure 6.6b: link to virtual reality model from which Figure 6.6a was taken. |
Figures 6.7a and b, 6.8a and b suggest
how that model was used: colored buildings are added, only on prime
parcels, according to numbers of residential units to be added and to guidelines
suggested by Taskforce members (selected for expertise in construction,
urban planning, architecture, and so forth). Different building colors
respond to different particular suggestions. This set of four models
represents merely one possible scenario; input from numerous sources was
important in creating a variety of alternatives for policy makers to consider.
Figure 6.7a. Downtown Ann Arbor buildings extruded from footprints digitized from aerial. Gray buildings are existing buildings. Yellow buildings are built on empty lots or on surface parking lots. Blue buildings are built along Huron Street (possibly as replacements for, or on top of, existing buildings). Red buildings are built with upper story setbacks on a subset of streets identified by the Taskforce. The number of new buildings is sufficient to support 1000 new residential units. All non-gray buildings are built on prime parcels. Figure 6.7b: link to virtual reality model from which Figure 6.7a was taken. |
Figure 6.8a. Downtown Ann Arbor buildings extruded from footprints digitized from aerial. Gray buildings are existing buildings. Yellow buildings are built on empty lots or on surface parking lots. Blue buildings are built along Huron Street (possibly as replacements for, or on top of, existing buildings). Red buildings are built with upper story setbacks on a subset of streets identified by the Taskforce. The number of new buildings is sufficient to support 2500 new residential units. All non-gray buildings are built on prime parcels. Figure 6.8b: link to virtual reality model from which Figure 6.8a was taken. |
Virtual reality models served to pique
conversations and help Taskforce members to visualize alternatives.
Eventually, they saw a need to compare one virtual reality model to another.
For that purpose, "viewpoints" were inserted into the VR models (find the
"viewpoints" pull down in Figures 6.6b, 6.7b, 6.8b, so that different models
could each be viewed from exactly the same vantage point (guided by the
computer). While the insertion of viewpoints was helpful, direct
comparison still required retention of a great deal of visual information
in one's memory. Animation of the models of the DDA, as in Figure
6.9 offered a way to look at multiple global alternatives.
Figure 6.9. Animation of various alternative screen captures from multiple VR models permits consistent visual comparison of models from one vantage point. |
Thus, the solution for local views was
also to take screen captures from the same viewpoint of different VR models
and stack them in an animation. The 3D VR models above were built
on May 27, 2004. Earlier models were shown to the public on April
27; public reaction was used to create a responsive model on May 3.
The May 3 model was used in conjunction with the April 27 model as a stacked
animation built from the taller April 27 model fading into the shorter
response model. The results were presented to the Taskforce, May
10. as in Figures 6.10, 6.11, 6.12, and others. These exemplify the
idea of using animation to make clear visual comparisons by taking screen
captures from VR models from the same viewpoint: the VR models might
all be from the same time, as in Figure 6.9, or they might be from different
times as well, as in Figures 6.10, 6.11, and 6.12.
Figure 6.10. Animation of various alternative screen captures from multiple VR models permits consistent visual comparison of models from one vantage point. |
Figure 6.11. Animation of various alternative screen captures from multiple VR models permits consistent visual comparison of models from one vantage point. |
Figure 6.12. Animation of various alternative screen captures from multiple VR models permits consistent visual comparison of models from one vantage point. |
These models, and results from hundreds of others, were presented to the Taskforce in 11 different meetings in the spring of 2004. They were presented in a public hearing to the citizens of Ann Arbor on April 27, 2004 as chronicled in a front page story in The Ann Arbor News with a picture of a model on the front page. They were presented to the Mayor and City Council on June 7, 2004. A previous article in Solstice describes this activity in detail. On July 19, 2004, the resolution derived in part from these models was approved by City Council with a request for a special session in September subsequent to the opportunity for City Council to analyze the mass of materials. From sieve to virtual reality, the strategy employed in one local study condensed time across millennia.
*The author, S. Arlinghaus, acknowledges productive meetings on the Ann Arbor study with, and assistance from, the following individuals and groups (during the time work was done):