What does RMS Error represent?

RMS Error, or Root Mean Square Error, is a statistical measure used to quantify the difference between values predicted by a model or an estimator and the values actually observed. In the context of GIS, it specifically represents the average of the distances between the mapped location (the predicted location) and the actual location (the observed location). This metric is particularly valuable because it provides a single, understandable number that reflects the accuracy of spatial data by considering the deviations in both directions—underestimates and overestimates.

This average calculation involves taking the square of each individual distance (to eliminate any negative values), summing those squared distances, and then dividing by the number of observations to find the mean. The square root of this mean gives the RMS Error, which restores the original units of measurement. Thus, it effectively summarizes how much, on average, the data points differ from their true locations.

Choosing RMS Error allows GIS professionals to assess the accuracy of spatial representations and make informed decisions about data quality, which is crucial for reliable analysis and decision-making.