[Objective] To determine the optimal statistical unit

analyze the spatial distribution of topographical relief in Shaanxi Province in order to provide basic data for the classification of geomorphic types.[Methods] Based on the 90 m resolution SRTM(shuttle radar topography mission)

DEM (digital elevation model data)

the relief amplitude of Shaanxi Province was extracted with neighborhood statistics analysis. We selected 34 rectangular neighborhood windows (2×2

3×3

4×4

…

35×35) and 20 circular neighborhood windows(the radius ranged from 2 to 21)

and calculated the ratio of relief amplitude at different rectangular windows and circular windows. The optimal calculation unit was calculated by using the mean change-point analysis method. Classification map of relief amplitude in Shaanxi Province was obtained

and the features of relief amplitude were analyzed.[Results] The ratios of different topographic relief types varied greatly. The optimal statistical unit at rectangular neighborhood was 12×12

with an area of 898 704 m2

while the optimal statistical unit at circular neighborhood was R=8

with an area of 1 254 191.4 m2

indicating that the circular neighborhood was different from the rectangular neighborhood. Generally

the terrain in Shaanxi Province was relatively flat

and the relief amplitude was mainly at small and medium level.[Conclusion] The mean change-point analysis is an ideal method to determine the optimal statistical unit.