Spatial statistics Topic 4 2/2/2007

What is spatial statistics Not like traditional, a-spatial or non-spatial statistics But specific methods that use distance, space, and spatial relationships as part of the math for their computations Is a spatial distribution and pattern analysis tool Identifying characteristics of a distribution; tools used to answer questions like where is the center, or how are feature distributed around the center? (Measuring Geographic Distributions) Quantifying or describing spatial pattern; are our features random, clustered, or evenly dispersed across our study area? (Analyzing Patterns) Mainly deal with point, line, polygon (vector) Why use spatial statistics? To help assess patterns, trends, and relationships Better understanding of geographic phenomena Pinpoint causes of specific geographic patterns Make decision with high level of confidence Summarize the distribution in a single number

Measuring geographic (spatial) distribution Used to Compare distributions of different features Identify directional trends of features Examine changes over time

Analyzing spatial patterns Analyzing Patterns Global calculations Identifies the patterns/overall trends of data Are features clustered and what is the overall pattern? Spatial Autocorrelation tool Mapping Cluster Local calculations Identifies the extent and location of clustering or dispersion Where are the clusters (or where are the hot spots)? Hot Spot Analysis tool

Z score is a measure of standard deviation. If you have σ is (-1.96, 1.96), z score is falling between them, you are seeing a pattern of random pattern. If z score falls outside, like -2.5 or 5.4, then you have a pattern that’s too unusual to be a pattern of random chance

Followed with a free ESRI video presentation “understanding Spatial Statistics in ArcGIS 9” by Sandi Schaefer and Lauren Scott.