# Average Nearest Neighbor tool extreme restuls for different area?

I'm using the "Average Nearest Neighbor" tool in ArcGIS 10.3 to calculate whether my point feature class is clustered, random or dispersed.

One of the parameters is area. I tried putting different areas and discovered that if I cut the area lets say by 50% the result changes form clustered (one extreme of the graph created by the software) to dispersed (the other extreme of that very same graph).

Can someone please explain how area is being used by ArcGIS to calculate that? As far as I knoe Nearest Neighbor has nothing to do with area it's all about the distance between the points.

• From the tool notes, area is the size of the study area. If you reduced it by 50%, it may not be using all the data. Apr 14, 2016 at 16:56
• that can explain it. Although in terms of size it is absolutely enough. Is there a way to tell it where (which corner) to start the area from? Apr 14, 2016 at 16:59
• @mkenned As I recall, the tool will use all the data. The numerical value of the area is used to estimate expected intensities. If you input an large area, the expected intensities will be low and so the actual intensities will seem too high in places, leading to a determination of "clustering." If you input a small area, the expected intensities will be high and the actual intensities will be generally too low, leading to a determination of "dispersed." Unless the study region was determined a priori, this "area" input is arbitrary, making the tool practically worthless--and even deceiving. Apr 14, 2016 at 18:36

``````expected mean nearest neighbor distance = 0.5 * sqrt(area / n)