A geospatial modeling system (20) may include a geospatial database (21) for storing geospatial data points each having respective elevations associated therewith. The system (20) may further include a processor (22) for data thinning the geospatial data points by selecting discriminant points therefrom. The processor (22) may select discriminant points based upon: (a) identifying a current patch having a plurality of spaced-apart current geospatial data boundary points; (b) selecting a current discriminant point within the current patch based upon sequentially stepping through the geospatial data points therein to determine respective elevation differences relative to the current geospatial boundary points and comparing the elevation differences to a threshold range; (c) identifying a plurality of new patches, each having a plurality of spaced-apart new geospatial boundary points including the current discriminant point; and (d) iteratively repeating steps (b) and (c) for each of the new patches until no further new discriminant point is selected.