Surveying GIS-Why Should I Record My Survey?
March 1, 2007
How many times have you heard the question “If not the surveyor, then who?” It’s certainly a fair question. Unfortunately, it goes unanswered all too often, even by the surveying community.
Though many jurisdictions have laws and ordinances requiring surveyors to record their surveys as public documents, some haven’t yet realized the value of the surveyor’s role in a public cadastre.
Technology has modernized the way surveyors do their work. Improved products tend to raise the level of expectation all around, which has resulted in the desire for a “survey-accurate GIS.” This leads to the question, “Who should have the oversight responsibility for a survey-accurate GIS?” And we are brought inexorably back to “If not the surveyor, then who?”
Many of us who practice land surveying with an emphasis on GIS didn’t start out that way. Some of us started out as plain, ordinary “dirt surveyors” who simply wished to improve our lot, so to speak. Since then, more than a few feet of water has passed under the first bridge we ever staked out. And here we are, in the future.
Revenge of the NerdsNot all that long ago, when GIS moved in as the “new kid on the block,” some in the survey profession didn’t take it seriously and others considered it a threat. Unfortunately, there are still hard-core pockets of both attitudes remaining. A good deal of the criticism leveled at early GIS projects was valid. Most of those early systems were constructed by IT types with little or no input from surveyors. Those folks, though well-intentioned, were generally deficient in their knowledge of property surveying and its relationship to map construction. So they didn’t anticipate or consider two very critical elements of GIS: (1) that the data in the source documents were often less than perfect, and (2) that some users would apply those virtual values to real-world projects under the assumption they were the standard.
That was then, this is now, and most concede GIS is now part of the mainstream of the surveying and mapping landscape. But along with that comes many new responsibilities. Yes, there are now expectations to reckon with.
The “honor system” of standardization hasn’t proved to be an effective method. Any “system” whose parts are created independently logically requires some form of central coordination. Eli Whitney was arguably the first American to realize this when he procured a contract to mass-produce 10,000 “stands of arms” for the fledgling American Army. Though he hired the very best craftsmen available, some of the assembled muskets had a minor problem. They couldn’t fire a round. Though the independently produced component parts were meticulously honed and crafted, they didn’t integrate well with other component parts, mostly due to interpretation.
What is often misunderstood in the integration of survey data into a geographic information system is the difference between fit and function. For a long time, many early developers assumed that independent land surveys would simply dovetail perfectly in their revolutionary new product. Surveyors knew better, but no one was listening.
They weren’t listening because accuracy wasn’t particularly relevant in those early systems. So GIS mapmakers proudly produced “pretty” maps that depicted their imperfect data sets as a finished product. There was just one small problem--most of those data sets needed a lot more attention to make them whole, complete and “accurate.” And it didn’t take long for these flaws, imperfections and deficiencies to surface.
What most laymen and far too many surveyors generally fail to understand is the difference between the cartographic representation of data sets and their actual values. Typically, only the GIS data managers are aware of this dirty little secret. But as the data gets used, and in many cases misused, this unfortunate fact becomes exposed, sometimes with serious consequences.
The Monolithic Parcel FabricOne of my old party chiefs had a colorful way of describing property maps showing laps and gaps: “This here plat looks like my grandma’s teeth.” I can only imagine how he might have reacted to a GIS parcel layer with all of its mismatches accurately rendered.
In theory, all boundary lines abut and match perfectly. But the only place that ever happens is in theory. In the real world, a parcel layer more often looks like a jigsaw puzzle put together from the pieces of disparate sets. Surveyors naturally understand this. Laymen and far too many GIS professionals and IT types do not.
Maps that require rendering the landbase to show its relationship to other features require a vehicle. That vehicle in GIS is known as symbology. Symbology is a catch-all term that indicates a value used as a “symbol” to represent a feature on a map.
Surveyors have rules that determine how we conduct our business. So do cartographers. GIS layers are constructed from a database of individual elements presumed to be individually complete and correct. And in the case of land surveys, they usually are.
But we have a conundrum. These complete and correct surveys don’t form a monolithic parcel fabric when placed in a database and rendered cartographically. Earlier I mentioned surveyor’s rules. Those were all ostensibly applied before any of the surveys were entered into the GIS database.
Cartographers and software programmers have rules to follow as well. And this is where the rub lies. The cartographer knows he has a more “general” audience. His symbology needs to be understood by the layperson as well as the professional.
GIS software uses a process called topology (I have covered this in a previous column; see “Surveying GIS,” POB August 2004.) Topology builds the layers to appear monolithic whether or not the underlying geometry supports it or not. The end product becomes generalized and is presumed easier for the layperson to interpret. It is assumed that the professional will drill down into the data for more precise answers.
Historically, of course, this has not been the case. Some databases have been over-generalized by a combination of both poor data and poor data analysis. This is what is typically referred to as “rubber sheeting" and was once the only solution GIS developers had to deal with survey information that didn’t mesh. And everyone should know by now, all surveys are not going to mesh.
Land Development Digital Submittals and the Global NetworkGenerally speaking, the landbase in a GIS is largely the product of the work of surveyors in one form or fashion. And that should make for a good, solid, accurate land base, right?
Well, not exactly. In many cases the surveyor’s work is nearly unrecognizable due to the influence of a middleman, such as a GIS practitioner who may have little or no survey knowledge.
GIS professionals use two general methods to get survey data into a database. In the better systems, the data on the map is “cogo’d” in. There are even error handling procedures for surveys that (heaven forbid!) do not close mathematically. Some hard copy maps are simply scanned and digitized to “best fit” whatever is in the database with little or no regard for how things match on the ground.
A better solution to the survey-accurate GIS is the digital submittal. Technology in GIS/CAD has advanced to the point where the two integrate well.
Digital submittals can actually be beneficial to the survey community. When a GIS landbase map layer is created, it is typically constructed from various types of source material. In the modern world we have created an urgency to keep data current. To be sure, it’s still good to have a paper trail. But editing basemap layers can be significantly expedited through the use of digital submittals. This helps to keep the system current and makes new data available to the survey community sooner.
How Much of my Data Ends Up in a GIS?There has been a long-held misconception that when a surveyor’s work gets incorporated into a GIS, or otherwise attached to a GIS, he is allowing others to distribute his survey. That is not the case. The framework of his survey is incorporated into a GIS, but the recorded document maintains its own separate identity in the file.
Many agencies keep the original hard copy plats and maps in vaults in perpetuity. Some provide copies in a variety of formats. Some of the formats are “digital” in nature, but they are distributed in TIFF (Tagged Image File Format) or PDF (Portable Document Format) and certainly not in the author’s original intellectual property.
Real-Time Correction Services for CORSThis is a giant leap forward in the development of a “survey accurate” basemap layer. Costs have made tying property surveys to the grid prohibitive in the past in many areas. As GPS was introduced, more emphasis was placed on acquiring and requiring positions on land surveys. But time and cost were still important factors.
More recently, correction services have been developed that produce great accuracy with little or no processing time. Many municipalities and transportation departments have been implementing these services for their staffs and making them available to private surveyors.
So, let’s return to the original question, “If not the surveyor, then who?” What then stands in the way of a survey-accurate GIS? Sadly, there are far too many jurisdictions that have not recognized the value of an automated map and records system. They have not yet recognized that the benefits of recordation far outweigh any perceived disadvantages. Let us hope for the future of the surveying profession that this changes.
Terms to KnowSymbology: the set of conventions, rules or encoding systems that define how geographic features are represented with symbols on a map. A characteristic of a map feature may influence the size, color and shape of the symbol used.
Topology: the defining spatial relationships between features.