Calculating Quadrat Analysis and the Poisson Distribution using ArcGIS Pro and Excel

Like ANN (Average Nearest Neighbor) Analysis, Quadrat Analysis is another descriptive metric to measure the distribution of a set of points. Instead of calculating Euclidean Distance between each point and its nearest neighbor, Quadrat Analysis overlays equally-sized polygons (called Quadrats), runs a spatial join and summarizes the frequency to compare the counts/frequencies versus a Poisson Distribution, a discrete probability distribution. Both of these graphs (the Observed Distribution vs. the Expected/Poisson Distribution) make powerful visuals and the Kolmogorov–Smirnov test can calculate statistical differences between the graphs created from each of the calculations. The value of Quadrat Analysis is twofold: 1) The overlaying of equally-sized quadrats make for powerful visualizations using polygons that do not need to be normalized for area and 2) It applies existing statistical calculations to determine statistical significance.

These videos have been created in support of teaching and research in the field of GIS (Geographic Information Systems) for the Department of Environmental, Earth and Geospatial Sciences at North Carolina Central University (NCCU). Established in 1910, NCCU is located in Durham, North Carolina, and serves about 8,500 students. The mission of our department is to promote intellectual, professional, and personal excellence through the highest quality instruction, research, and service in the environmental, earth and geospatial sciences. Its vision is to be recognized as a regional, statewide, and national resource for students and society as well as professionals who work in the many fields that are encompassed by the environmental, earth, and geospatial sciences. Students in our programs currently focus their studies in the fields of seismology, natural hazards, GIS (Geographic Information Systems) and Remote Sensing applications, environmental health & impacts and remediation technology among others. Our courses are designed to provide students with the analytical and methodological skills necessary to understand or derive explanations for individual occurrences, for recurring processes, and for invariable as well as statistical regularities in the earth’s lithosphere, hydrosphere, atmosphere, and biosphere. The department prides itself in former students who fostered these skills and have gone onto successful careers in the field at places such as the North Carolina Department of Transportation, City of Durham, Environmental Protection Agency, Lowe’s Corporation, Environmental Protection Agency, National Forest Service, Army Corps of Engineers, real estate firms and private contractors or students who have gone onto Ph.D. programs at places such as North Carolina State University, North Carolina A&T State University and the University of North Carolina, Greensboro.