Most potential users of the Spatial Calculator will immediately ask one question: How accurate are these calculated latitudes and longitudes? Clearly, the calculator cannot achieve the sub-meter accuracy level of GPS technology. But, neither does it require the significant investments of GPS. The following factors influence the accuracy of the Spatial Calculator's results.

The Base Map: The base map of latitudes and longitudes that is being used by the calculator is a landgrid database that belongs to Topographic Mapping Company (TMC) of Oklahoma City. TMC originally created this database by digitizing section lines from the USGS 7.5 minute (1:24,000) quadrangle maps for the State of Oklahoma. This scale allows an assumed accuracy within 40 feet.

The Datum: The USGS maps, and therefore the original landgrid database, were based on the North American Datum 27 (NAD27). We have recalculated the entire landgrid database to NAD83, so users have the choice of either datum. (NAD27 is based on an ellipsoid model of the earth with a fixed base point of Meade's Ranch, Kansas. NAD83 is based on a more recent ellipsoid model that was derived from satellite measurements of the earth with the correct equatorial and polar radii.) To maximize your map accuracy, you will want to match the datum for any other features you might be mapping along side these calculated points. If you are not sure which datum to use, choose NAD83.

The Quartering Process: It would be easy if the Public Land Survey System (PLSS) was a perfect grid of one-square-mile sections (5280 feet by 5280 feet) that we could partition into four equal quarter sections. Since it is not, we have implemented a quartering methodology as follows.

Since this quartering process has so many complexities, there are probably ways in which our methodology could be improved. We welcome user input that would help us refine this quartering process. Please contact us if you have any suggestions or questions.


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