1 Uncertainty in Extrapolations of Predictive Land Change Models R Gil Pontius Jr Joe Spencer Prepared for presentation at the Open Meeting of the Global Environmental Change Research Community, Montreal, Canada, October, 2003.

2 Major Points Validation is a waste of time, –unless you use the validation statistic to express the level of certainty of predictions of the unknown. The prediction’s accuracy approaches random as the prediction’s time interval grows. –We estimate how fast the accuracy approaches random.

3 Worcester Massachusetts and nine surrounding towns

4 Strategy of Three Runs

5 Percent Built versus Geology 1971

6 Percent Built versus Geology 1985

7 Percent Built versus Geology 1999

8 Percent Built versus Slope 1971

9 Percent Built versus Slope 1985

10 Percent Built versus Slope 1999

11 Real Built 1971

12 Simulated Built

13 Real Built

14 Observed Accuracy Run 1: % 6%

15 Estimated Accuracy

16 Strategy of Three Runs

17 Expected Accuracy

18 Expected Accuracy Run 2: % 6%

19 Real Built 1985

20 Simulated Built

21 Real Built

22 Accuracy Run 2: 1999 Observed 1% Quantity Error 9% Location Error Expected 4% Quantity Error 6% Location Error

23 Expected Accuracy Run 3: % 9%

24 Simulated Built

25 Expected Accuracy

26 Expected Accuracy

27 Major Points Validation is a waste of time, –unless you use the validation statistic to express the level of certainty of predictions of the unknown. The prediction’s accuracy approaches random as the prediction’s time interval grows. –We estimate how fast the accuracy approaches random.

28 Method is based on: Pontius Statistical methods to partition effects of quantity and location during comparison of categorical maps at multiple resolutions. Photogrammetric Engineering & Remote Sensing 68(10). pp PDF file is available at or National Science Foundation funded this via: Center for Integrated Study of the Human Dimensions of Global Change Human Environment Regional Observatory (HERO) Plugs & Acknowledgements