Metric? or what? Our assessors are required by law to inspect personally every 3 years. While much of that is cursory, they do measure, they do locate new construction, new add ons, and new outbuildings with a digital aerial photo system. I don't know if they have changed to laser (prolly) but in the late 90s they were using a well worn appraisers tape because on the Board of Equalization, I went out and helped the chief residential appraiser measure a house being contested (and the homeowner was right about the upper floor measurement.) But their measurement of the ground floor was right on...to the foot.
I do not understand the concept of extracting the stairwell out of GLA...and our assessors don't. To me stairs are a nothing-burger. "Gross" means exactly that. It doesn't imply closest and stairwells need to be removed. It implies the exterior footprint of a house. Be it measured with a precision of 1 foot or a tenth of a foot, if fractal geometry taught me anything it is that the measurement of anything changes with the size of the measuring stick. Measuring the coast line of Ireland with a measuring wheel on a map will give a different result measuring with a yardstick on the ground. Scale is a function of precision, not accuracy.
I've only examined assessor sketches in 3 states and roughly 12 or so counties, but all were to the foot and all were reasonably accurate most of the time. My home county is commonly very dependably correct....to the foot. They measure only from the outside, as we should. Therefore stairwells are nothing. The upper floor? You have to do the best you can, that's all. The idea you measure to a precision of 0.1' a foot only to guess at wall thicknesses and measure the upper ½ story from the interior is mixing two precisions of accuracy which requires you to default to the less precise measurement...and getting closer than a half foot on the upper level of a 1½ story home sees a mite close to "false precision".
