GIS and Online Mapping: Stretching the Truth Scale

When I began my land planning career in 1968, one of the first things I learned about was the use of the Rubber Scale. What is it? Rubber Scale was a term used by civil engineers and land surveyors to describe an inaccurate plan that ignored the physical limitations of the existing terrain. To say that the planner or architect had used a Rubber Scale to create a beautifully rendered plan with pastel colors and soft shadows cast from tree stamps was a negative comment, since these plans were pretty much worthless to the engineer and surveyor that had to make the plans conform to regulations. Because the lines were hand drawn back then (and in many cases still are today), accuracy was, and remains, an issue.

I was guilty of ?stretching the scale? to maximize density, thus the term. The rubber scale was beloved by designers who wanted to look good to their developer clients. The developer expected a plan that maximized yield, and a plan that was of a higher density than they expected would surely be pleasing. Of course, these plans had no basis in reality. Ultimately, the land surveyors and civil engineers would lose the units we falsely claimed, and they would also get blamed for the density loss!

Fast forward two decades to 1988, when GIS (Geographic Information Systems) began gaining market share. Government agencies (typically cities and counties) embarked on spending sprees with the promise of a new era in planning technology brought on by the advent and proliferation of the GIS technology, which blended graphic mapping information with a data base. You wanted to know property information, demographics, soil types? Just query the map. The sales teams of GIS mapping systems convinced those in charge of purchasing that ?parcels? shown on the map could be traced quickly from a variety of sources, then later ?rubber sheeted? into accurate surveyed section corners. As if by magic, inaccurate parcels would be made precise.

So? early, existing hand drawn maps were traced into a computer, and the imprecise data was made even more imprecise. Even when the data came from aerial maps, created by flights several thousand feet above the surface, the accuracy was at best within three to five feet of actual location. What happens to curved boundary lines if the map is stretched to meet tens of thousands (or more) of lot corners, with all four section corners set accurately? The answer is, of course, a map that would be impractical to correct at a later date. Very few GIS maps exist today that were done using accurate land survey from the beginning.

Fast forward another two decades and more to today, when Google Earth and its rivals, MapQuest and BingMaps, have unfortunately become the basis for site information. Call the data of these suppliers ?on-line graphics?. There are a variety of software systems that boast that site layout can easily be done using on-line-graphics, or simply using the available on-line GIS mapping data.

Here lies today's problem: None of this information is likely to be accurate enough to be useful to an engineer or surveyor who ultimately must put their license on the drawing, guaranteeing its accuracy.

GIS salesman make their sales commissions by convincing the world's governments that data can be ?adjusted? later to a more accurate data structure. This is true, but not economically feasible or practical. Since curved property lines are represented in a GIS system by a series of miniscule lines, it could be possible for the data to be corrected. This is like saying that it could be possible to temporarily build an approximate building and later on move walls to the locations shown on the plan. It would be possible, yes, but hardy cost (and time) effective.

A lack of correct information is a huge problem when using GIS or on-line-graphics information. For example, it?s not possible to see contour lines that are accurate enough to determine flood plain, wetlands, or other information critical to the initial site design. Even when this information is shown on the city or county on-line map, what is the source of that data? Most of these maps are sourced to the lowest bidder. Was that wetland shown on the site just something that looked wet on an aerial map traced by a low-bidding draftsman, or was the wetland defined by an environmental expert who accurately surveyed it and somehow placed it precisely on the GIS map? This is the modern day version of using a rubber scale to measure the very data used to make decisions. Entire cities are stretched beyond practical use by surveyors and engineers.

Many think that the on-line-graphics are taken from a satellite in space with some military camera that spy agencies use. Wrong! The images are derived from aerial mapping firms. These photographs might be several years old, which is why you might look at a newly developed suburban area, while the map still shows a farm field. You could be looking at a site to build residential units, not realizing a sewage treatment plant was recently built next door.

Building Information Modeling (BIM) is a way for architects, engineers, contractors and owners to communicate and collaborate while designing a structure they are all involved in creating. The various parties can be instantly communicating worldwide on a single project located anywhere. Recently, I was participating in an on-line conference from one of the suppliers of BIM technology, who wanted to sell me on the idea of using BIM as an additional tool to use with our precision site design software. I require a developer to furnish us with an accurately surveyed boundary, topography, and any wetlands delineated precisely on the site before I begin my work. The BIM supplier took an office building from Florida (created accurately), and placed it on a site in South Dakota shown by Google Maps as if somehow that?s all there is to planning. Nowhere in the conversation did the salesman mention local regulations, site restrictions, where any easements might be (most often easements are not easily seen in photographs), etc. As soon as I was shown how a building from Florida could be placed on a site in a northern state using an on-line-graphics data base as the planning solution, the demonstration was over. Could BIM be used for site design? Absolutely, but only by using precision data from qualified engineers and surveyors, not on-line-graphics.

The tax payers have financed billions of dollars worth of GIS systems with map data of questionable accuracy, with the understanding that the rough mapping data could be rectified accurately later. While true, the cost of converting existing maps would be prohibitive. The general public might think that these public data structures replace the need for land surveys and accurate civil engineering. But these vague images actually make it even more important to consult with a licensed professional to provide precision data before any design or development decisions are made.

Over four decades ago I was guilty of using the rubber scale. New technology has promoted us into a new problem, and moved us from a rubber scale to a rubber sheeted world.

Photo by edibleoffice: GIS of Hayes Valley, San Francisco.

Rick Harrison is President of Rick Harrison Site Design Studio and Neighborhood Innovations, LLC. He is author of Prefurbia: Reinventing The Suburbs From Disdainable To Sustainable and creator of Performance Planning System. His websites are rhsdplanning.com and performanceplanningsystem.com.