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 which, as a State university, contributes no funds to the city taxpayer economic base), and PUD is for Planned Unit Development. In Figure 1, the animated map shows the City of Ann Arbor parcel map colored as a thematic map by zoning category: the broad PL zoning is part of the central campus of the University of Michigan. The curved line near the left side of the map. representing the Ann Arbor Railroad corridor, has most of the manufacturing parcels adjacent to it. Separate categories enter the picture in sequence, arranged according to alphabetical ordering of zoning category. The coloring scheme is exhaustive: every parcel is covered. It is also mutually exclusive: no parcel has more than one color. Thus, the zoning classification serves as a geometric partition of the parcels.
Figure 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.
Once an inventory of parcel categories is obtained by creating thematic maps, the groups of parcels will be removed in accordance with various ideas. The goal is to select targets of opportunity for taller projects as illustrated below.
Figure 2. Zoning categories, DDA boundary, railline, floodway and floodplain.
The current interest is to consider only zoning categories, as the downtown
"core," of C1A, C1AR, C2A, C2AR, C2BR as those containing parcels
that are targets of opportunity for building structures of height greater
than that permitted by FAR. The current FAR in these categories is either
200 or 300. The idea is that there may well be parcels within these
core downtown areas that could support height in excess of that permitted
by the FAR. In Figure 3, the shading is removed for these zoning
categories; they are easily focused on as a grouping. When parcels
containing historic district designation (and relatively short buildings)
are superimposed on the pattern in Figure 3, further limitation of targets
of opportunity is the result (Figure 4). The historic district parcels
were inserted in a separate step because they overlap the standard zoning
hierarchy and are not a part of the geometric partition noted above.
Figure 3. Shading is removed from C1A, C1AR, C2A, C2AR, C2BR zoning categories--the downtown core--to visually group these regions as those containing parcels that are targets of opportunity for height in excess of that permitted by the FAR.
Figure 4. This map is identical to the map in Figure 3 with historic district parcels superimposed in red. The historic district designation further limits the targets of opportunity.
A current suggestion by the Planning Department staff and the Ordinance
Revisions Committee is to use the street hierarchy to select general target
areas: wider streets support taller nearby structures. Thus,
the zoom-in of Figure 5 is on Huron Street, the widest street in the DDA.
Use of the aerial not only permits quick determination of where parking
lots and existing buildings are located but it also shows shadow pattern
of existing buildings suggesting guidelines for upper story setbacks and
other tools that limit reduction of light. Light in the streetscape
is pedestrian-friendly (and vegetation-friendly), particularly at this
mid-continental latitude. Highest priority immediate targets of opportunity
for height in excess of that permitted by the FAR thus appear (from the
abstract representation in Figure 5 alone) to be in the large parking lots
visible along Huron Street, with suitable upper level setbacks to minimize
shadow in the street. Further analysis is needed, however, to include
steep slopes, opinion from members of the public and from developers, the
will of governing bodies, and various other acadmic and non-academic factors.
Figure 5. Zoom in--use the street hierarchy to suggest locales--notice the shadows leaning out into Huron Street as well as the content of the core area along Huron Street, from tall buildings to parking lots.
Dynamic maps, produced in Geographic Information Systems (GIS) software, when coupled with high quality aerial photography produces powerful visualization capability that can guide decision-makers. One limitation of this visual analysis is dimensional: even though the aerials are high quality, one still really has only a two-dimensional view of a three-dimensional scene. The ideal would be to have dynamic three dimensional models of the core area. Virtual reality (VR) affords such an opportunity in two different ways: through web-based virtual reality and through immersion in a virtual reality CAVE. Only the former technique can be displayed in this article. The plan, beyond the VR experiments in this article, is to take files such as these, place them in the CAVE in the Media Union at The University of Michigan North Campus in Ann Arbor, and invite policy makers to immerse themselves in the virtual reality created by alternative height scenarios (report to come in a subsequent issue of Solstice) in order to consider the issue of a maximum height ordinance or any other zoning issues in the downtown.
To view the VR experiments below (Figure 6), first download Cosmo Player
and install it in your browser according to directions. Then, click
on the links below and practice navigating through the streets of downtown
|FAR Virtual Reality:: translucent buildings are superimposed, lot line to lot line on parcels in the downtown core zones. This VR experiment depicts the downtown with the simplest use of the FAR. [The DDA region is shown in black; the Allen Creek floodplain in blue.]|
|Actual height Virtual Reality: again, buildings are superimposed, lot line to lot line, on parcels in the downtown core zones. This VR experiment depicts the downtown using actual building heights, where known. [The DDA region is shown in gray; the Allen Creek flooplain and floodway in shades of blue; building color is according to height category.]|
|Figure 6. Virtual Reality experiments performed using ArcView GIS, v. 3.2, with Spatial Analyst Extension and 3D Analyst extension (from ESRI)..|
The author acknowledges productive meetings with and assistance from
Software used: ArcView GIS, v. 3.2, with Spatial Analyst Extension and 3D Analyst Extension. All from ESRI (Environmental Systems Research Institute, Redlands, CA).