A computer implemented method of determining an error radius for a calculated position, comprising: providing a data structure including a plurality of first fields identifying a scaled geographic area based on a global projection reference system, the system divided into scaled geographic areas and having multiple levels of areas of different size, and a plurality of second fields identifying, for each of the first fields, a position error radius associated with a scaled geographic area and level, each position error radius calculated to be a maximum error radius for at least a threshold percentage of inferred positions in the associated scaled geographic area; determining a scaled geographic area associated with the calculated position; and returning a corresponding error radius mapped to a scaled geographic area from the data structure which is associated with the calculated position, the error radius indicating a potential variance in the calculated position, wherein providing the data structure comprises: receiving position survey information for a venue; determining an error radius for each of a plurality of first inferred positions based on a first data set; determining an error radius for each of a plurality of second inferred positions based on a second data set; and determining (650, 655) a correlation between each determined error radius based on the first data set and the second data set for each inferred position above the threshold percentage, the threshold percentage being a percentage error. providing a data structure including a plurality of first fields identifying a scaled geographic area based on a global projection reference system, the system divided into scaled geographic areas and having multiple levels of areas of different size, and a plurality of second fields identifying, for each of the first fields, a position error radius associated with a scaled geographic area and level, each position error radius calculated to be a maximum error radius for at least a threshold percentage of inferred positions in the associated scaled geographic area; determining a scaled geographic area associated with the calculated position; and returning a corresponding error radius mapped to a scaled geographic area from the data structure which is associated with the calculated position, the error radius indicating a potential variance in the calculated position, wherein providing the data structure comprises: receiving position survey information for a venue; determining an error radius for each of a plurality of first inferred positions based on a first data set; determining an error radius for each of a plurality of second inferred positions based on a second data set; and determining (650, 655) a correlation between each determined error radius based on the first data set and the second data set for each inferred position above the threshold percentage, the threshold percentage being a percentage error. receiving position survey information for a venue; determining an error radius for each of a plurality of first inferred positions based on a first data set; determining an error radius for each of a plurality of second inferred positions based on a second data set; and determining (650, 655) a correlation between each determined error radius based on the first data set and the second data set for each inferred position above the threshold percentage, the threshold percentage being a percentage error.