Accuracy in Surveys (2)

You may find this definition of accuracy to be odd. How can two numbers BOTH be correct just because they are close to each other? This strange definition points to the fact that it is impossible to know the exact correct area. Each survey is a more or less accurate approximation of the actual area. It would be nice if after a survey, we could magically compare our result to the ‘true’ number – but this is not the case. We will always have to live with some degree of inaccuracy. According to BOMA, the acceptable limit is 2%. Using the building example from above, this would mean that there would still be $180,000 'up for discussion' each year. Even though this is the allowable limit of the accepted standard, our goal is to be significantly more accurate than this.


What are the causes of survey errors and why would the industry have a tolerance for a relatively large degree of error? Error and variation are caused by several different factors that can and do occur together. The first and most serious is human error - mistakes. People get confused, they measure from the wrong surface, they incorrectly record basic elements and they can transcribe and garble the information that their instruments provide. The second source of error is mechanical measurement error. Devices such as tapes can become stretched and worn. Laser devices can go out of calibration. A third source of error is the variations that occur in building construction. Walls are not straight, consistent or smooth. Structures are not built exactly according to plan. Very subtle angles and variations over long distances can lead to significant differences in interpretation of area. Finally we believe that the methodology, the strategy used to record information and to reconstruct it on a computer can also have a profound effect on the accuracy of the final calculations. Given all these sources of error, the industry has come to accept a variation of up to 2% as being a ‘high quality’ result.