spatial subsampling

1. https://arxiv.org/pdf/math/0503671

2. https://pro.arcgis.com/en/pro-app/help/analysis/geostatistical-analyst/an-introduction-to-sampling-monitoring-networks.htm

3. https://gis.stackexchange.com/questions/52365/creating-a-subset-of-points-shapefile-with-minimum-distance-between-points-in-ar

4. https://gis.stackexchange.com/questions/21616/select-maximum-number-of-points-more-than-x-meters-apart

5. https://desktop.arcgis.com/en/arcmap/10.3/tools/analysis-toolbox/near.htm

6. http://www.spatialecology.com/gme/

7. https://cran.r-project.org/web/packages/spatialEco/spatialEco.pdf

8. https://www.sciencedirect.com/topics/computer-science/spatial-sampling

9. https://automating-gis-processes.github.io/site/develop/notebooks/L3/nearest-neighbor-faster.html

      Describes the nearest neighbor approach used to generate the first subsample.
   

10. https://jakevdp.github.io/blog/2013/04/29/benchmarking-nearest-neighbor-searches-in-python/

       Describes the different params used to tweak the nearest neighbor approach.