Nearest Neighbour huge values QGIS 3.4

Question

I am repeatedly getting values in the 1000s for a nearest neighbour analysis in QGIS 3.4.

I've tested a different dataset and getting the expected result (i.e. between 0 and 2.5). But from the dataset I'm using I'm getting huge numbers:

Observed mean distance: 9.579807163911296
Expected mean distance: 0.0002003651354400665
Nearest neighbour index: 47811.747003144774
Number of points: 48
Z-Score: 633690.2583200812

A screenshot of the vector layer's points and the applied filter:

[1]: https://i.sstatic.net/etZkd.png [1]
[2]: https://i.sstatic.net/PEVJA.png [2]

The dataset can be accessed this OneDrive link: https://isbdragons-my.sharepoint.com/:u:/g/personal/ofidler_isb_bj_edu_cn/EXC4adHTCl5KlSP4UQNblYwBFb-7rO9-VLK367Uevgf_pg?e=LShz0z

My suspicion is QGIS isn't bounding the extent of the analysis properly. I've tried 'selected features only', which generated almost the same numbers. When I 'zoom to layer' it's the same extents as shown in the screenshot above.

Answer 1

Seems like layer extent is computed in degrees and distances in meters, or something else.

Project the layer to a projected CRS, which doesn't distort your distances much, to get reasonable values.

In QGIS 3.10.0 I can't see that behavior, but since QGIS 3.4.13 is the latest long-term release the question seems valid to me.