Spatial Technologies-GIS at the Site Level31 Jul, 2006 By: James L. Sipes
Technological advances in GIS enable design and planning in a range of scales
Mapping is the visual representation of data by geography or location-the linking of information to a specific place. In recent years GIS has become an invaluable tool in mapmaking, but it has been used primarily to show large areas such as cities or regions. That practice is changing, though, because the technology has developed to the point where it can be used effectively for making design and planning decisions at a variety of scales.
A Matter of Scale
Most design and planning projects fit one of three scales:
- 1. regional-scale projects that involve multiple communities and typically include thousands of acres;
- 2. community-scale projects such as vision plans, regional parks and greenways that are used by an entire community; and
- 3. neighborhood-scale projects that range from a couple of acres to hundreds or even thousands of acres.
"Traditionally GIS has not been used at the neighborhood level," says Pat Peters, senior associate in planning at EDAW, a design and planning firm with offices worldwide. "It has been much more widely used at the community and regional scale." Neighborhood- and site-scale projects include residential designs, parks and open spaces, urban plazas, streetscapes and commercial and industrial properties. These projects typically are the realm of architects, landscape architects and urban designers who are comfortable with site-scale design.
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"Planners are always looking at the bigger picture, such as how a site impacts the community," notes Peters, "while designers focus more on a particular site." Site designers typically follow a step-by-step process that includes inventory, analysis, design and implementation. Some designers take a more intuitive approach, and others are more pragmatic.
CAD has traditionally been the tool of choice for site designers because of the level of precision and detail that it offers. "CAD programs are excellent for producing accurate line drawings, but they are not very good at handling geospatial data," adds Peters. Most CAD programs are able to link graphic elements to database records, but this capability falls far short of data functionality available in most GIS programs.
Quality of Data
The perception of most designers is that GIS is intended for broad planning applications and isn't useful for more detailed projects. In the not-too-distant past, that perception would have been accurate. "A lot of effort went into creating data at the regional level," says Peters. "Now that we have built data sets at that level, there is more effort to produce more detailed geospatial data." Technologies such as LIDAR (light detection and ranging) can produce detailed elevation models that are extremely useful for site design. LIDAR uses pulsed-laser devices to record the distance from a camera to a given point using either ground-based or airborne sensors. The technology is still too expensive to be used specifically for a site-design project, but many municipalities are using LIDAR to create base information for their planning projects.
Figure 1. Designers and planners can use ærial imaging to help develop site plans. Image courtesy of Space Imaging
The higher the resolution of aerial imagery, the more detail can be identified (figure 1). Satellites from Space Imaging (www.spaceimaging.com), DigitalGlobe (www.digitalglobe.com) and OrbImage (www.orbimage.com) all can produce imagery with submeter accuracy. I recently used high-resolution imagery to develop a detailed master plan for a 500-acre site. The level of detail made it possible to identify ponds, vegetative patterns, existing roads and trails, eroded areas and manmade features such as cars, utility lines, and manholes.
With GPS technology, site designers have a tool that makes it easier to generate accurate, up-to-date information. GPS technology is not new, but it has advanced to the point where it is affordable and easy to use by even the smallest design firms.
Peters notes that one potential issue is that much of the data collected at the regional level, such as USGS (U.S. Geological Survey) DEM (digital elevation model) data, may be 10 or 20 years out of date. "For a recent design project, the base information we had was totally inadequate. Too often you don't really get the site-specific detail you need, such as grading, to site a building or lay out a road. A major building had been constructed on site, and there was massive grading associated with this construction." The DEM did not show any of these site changes and therefore was not useful for the project.
One concern is that designers may be using data that lacks the level of detail they need for site-level projects. "Using inadequate data can steer your analysis in the wrong way," adds Peters. Much of the analysis conducted in GIS is based on raster data because it's typically more effective for conducting overlay and buffer operations than is vector-based data. For many planning projects, a cell-based model of 5-10 meters may be adequate, but that's not sufficient for site-design projects. Site designers need data that has submeter precision.
On a recent project, I was working to identify entry points into a site, and the steepness of the terrain and existing streams were major concerns. I conducted the analysis using 10-meter data from USGS and wetland data from the National Wetlands Inventory, because that was all that was available. The site was surveyed a couple of months later, and the 2' contours and delimited streams and wetlands were significantly different from the data I initially used. This discrepancy resulted in major changes in the design proposals.
Making the Transition
Peters believes that one of the biggest limitations is that site designers have been trained in CAD, not GIS, and therefore don't know much about projections, date integrity, resolution and metadata. Also, it's common-place for surveyors to create a new base map for each site-design project. This survey helps ensure that a designer is working with the most accurate and up-to-date information. It also means, however, that designers don't need to learn about geospatial data available from other sources. Site designers should learn what geospatial data is important, how to obtain such data and what to do with it once they have it.
"GIS has evolved from a theoretical science, while CAD is more an applied science," Peters says. Programs like Autodesk's Map 3D will help blend the two sciences and make it easier for traditional CAD users to access GIS applications for site design. Many designers may find the transition to a program like Map 3D a little simpler because it's similar in look and feel to AutoCAD, the popular CAD program also from Autodesk.
Another reason that site designers have not fully embraced GIS is the perception that it takes too much time and energy to collect the data needed for site-level design. That perception is changing, however, as many cities, counties and other organizations develop extensive data sets for their respective areas, and this data is available for public design projects.
Many municipalities also prefer design submittals that are geospatially referenced. "Many county governments are now requiring that all design, planning and surveying projects fit into their existing GIS structure," says Peters.
Martin County, Florida, is one example. EDAW starting working with Martin County when it wanted to systematically examine how growth was changing the county's development patterns and how it affected the county's budget. The county requires that all design and planning projects be submitted in GIS format. The county uses ESRI's ArcView and ArcInfo for most of its GIS work, Kiva land records management system (www.accela.com/products/landmgt.asp) for working with tabular data, AutoCAD for CAD drawings and Hansen asset management (www.hansen.com) for integrating nonspatial data about assets.
Uses of GIS at the Site Level
The uses of GIS in site design are not markedly differently than in more traditional planning applications, such as rural planning, natural-resource management, and land-use planning. "Most of the work we have done with GIS in site-design work has focused on analyzing slopes, aspect, viewsheds and surface runoff," notes Peters. "The analysis itself is not that different from what we would do at a planning level."
By using GIS data, designers can develop a better understanding of a site. GIS helps add a level of intelligence to the maps that site designers can use for making decisions. For example, designers can identify which areas of a site are the steepest, driest or coldest. They can determine which spots have the best views, are the most buildable, and are the most environmentally sensitive.
Bill Miller, a design manager with ESRI, believes that GIS will change how designers approach projects. "Architects or designers involved in urban regeneration need to look at a 12- to 20-block area, and they need to look at a wide range of factors such as land-use suitability, noise, security analysis, green roof analysis and economics." Designers can go beyond the boundaries of a particular site and look at how that site fits into a larger context. For example, a 750-acre high-density residential site will have a tremendous impact on surrounding roads, schools and environmental conditions, and project designers need to understand these effects. This type of analysis requires a GIS topology with the precision of CAD.
Using GIS to access geospatial data also allows designers to consider a wider range of design options. The days of designing in a black box are gone. Concerned clients want to know not only what decisions are being made but also how and why they are being made. GIS provides the analytical framework that is needed to make site design systematic, measurable and defensible.
James L. Sipes is a senior associate with EDAW in Atlanta, Georgia, and the founding principal of Sand County Studios in Seattle, Washington. Reach him at firstname.lastname@example.org.