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LECTURE 8a_ SPATIAL STATISCAL ANALYSIS Mr. IdrissaY. H. Assistant Lecturer, Geography & Environment Department of Social Sciences School of Natural & Social Sciences State University of Zanzibar Introduction to spatial analysis Judging spatial association visually The concept of Clustering and Cluster analysis Spatial Cross-Correlation Pearson, Spearman Multivariate spatial association measures That Spatial Statistics, extends traditional statistics on two fronts. First, it seeks to map the variation in a data set and Secondly, it can uncover “numerical spatial relationships” within and among mapped data layers. Tobler’s Law “Everything is related to everything else, but near things are more related than distant things” 3 major benefits of spatial analysis Pattern Analysis Feature count Analysis 1. What is Cluster Analysis? 2. Types of Data in Cluster Analysis 3. A Categorization of Major Clustering Methods 4. Partitioning Methods 5. Hierarchical Methods 6. Density-Based Methods 7. Grid-Based Methods 8. Model-Based Methods 9. Clustering High-Dimensional Data 10. Constraint-Based Clustering 11. Outlier Analysis 12. Summary May 22, 2017 Data Mining: Concepts and Techniques 4 Cluster: a collection of data objects Similar to one another within the same cluster Dissimilar to the objects in other clusters Cluster analysis Finding similarities between data according to the characteristics found in the data and grouping similar data objects into clusters Unsupervised learning: no predefined classes Typical applications As a stand-alone tool to get insight into data distribution As a preprocessing step for other algorithms May 22, 2017 Data Mining: Concepts and Techniques 5 Pattern Recognition Spatial Data Analysis Create thematic maps in GIS by clustering feature spaces Detect spatial clusters or for other spatial mining tasks Image Processing Economic Science (especially market research) WWW Document classification Cluster Weblog data to discover groups of similar access patterns May 22, 2017 Data Mining: Concepts and Techniques 6 Marketing: Help marketers discover distinct groups in their customer bases, and then use this knowledge to develop targeted marketing programs Land use: Identification of areas of similar land use in an earth observation database Insurance: Identifying groups of motor insurance policy holders with a high average claim cost City-planning: Identifying groups of houses according to their house type, value, and geographical location Earth-quake studies: Observed earth quake epicenters should be clustered along continent faults May 22, 2017 Data Mining: Concepts and Techniques 7 A good clustering method will produce high quality clusters with high intra-class similarity low inter-class similarity The quality of a clustering result depends on both the similarity measure used by the method and its implementation The quality of a clustering method is also measured by its ability to discover some or all of the hidden patterns May 22, 2017 Data Mining: Concepts and Techniques 8 Dissimilarity/Similarity metric: Similarity is expressed in terms of a distance function, typically metric: d(i, j) There is a separate “quality” function that measures the “goodness” of a cluster. The definitions of distance functions are usually very different for interval-scaled, boolean, categorical, ordinal ratio, and vector variables. Weights should be associated with different variables based on applications and data semantics. It is hard to define “similar enough” or “good enough” the answer is typically highly subjective. May 22, 2017 Data Mining: Concepts and Techniques 9 Partitioning approach: Construct various partitions and then evaluate them by some criterion, e.g., minimizing the sum of square errors Typical methods: k-means, k-medoids, CLARANS Hierarchical approach: Create a hierarchical decomposition of the set of data (or objects) using some criterion Typical methods: Diana, Agnes, BIRCH, ROCK, CAMELEON Density-based approach: Based on connectivity and density functions Typical methods: DBSACN, OPTICS, DenClue May 22, 2017 Data Mining: Concepts and Techniques 10 Grid-based approach: based on a multiple-level granularity structure Typical methods: STING, WaveCluster, CLIQUE Model-based: A model is hypothesized for each of the clusters and tries to find the best fit of that model to each other Typical methods: EM, SOM, COBWEB Frequent pattern-based: Based on the analysis of frequent patterns Typical methods: pCluster User-guided or constraint-based: Clustering by considering user-specified or application-specific constraints Typical methods: COD (obstacles), constrained clustering May 22, 2017 Data Mining: Concepts and Techniques 11 Given k, the k-means algorithm is implemented in four steps: Partition objects into k nonempty subsets Compute seed points as the centroids of the clusters of the current partition (the centroid is the center, i.e., mean point, of the cluster) Assign each object to the cluster with the nearest seed point Go back to Step 2, stop when no more new assignment May 22, 2017 Data Mining: Concepts and Techniques 12 Example 10 10 9 9 8 8 7 7 6 6 5 5 10 9 8 7 6 5 4 4 3 2 1 0 0 1 2 3 4 5 6 7 8 K=2 Arbitrarily choose K object as initial cluster center 9 10 Assign each objects to most similar center 3 2 1 0 0 1 2 3 4 5 6 7 8 9 10 4 3 2 1 0 0 1 2 3 4 5 6 reassign 10 10 9 9 8 8 7 7 6 6 5 5 4 2 1 0 0 1 2 3 4 5 6 7 8 Data Mining: Concepts and Techniques 7 8 9 10 reassign 3 May 22, 2017 Update the cluster means 9 10 Update the cluster means 4 3 2 1 0 0 1 2 3 4 5 6 7 8 9 10 13 Strength: Relatively efficient: O(tkn), where n is # objects, k is # clusters, and t is # iterations. Normally, k, t << n. ▪ Comparing: PAM: O(k(n-k)2 ), CLARA: O(ks2 + k(n-k)) Comment: Often terminates at a local optimum. The global optimum may be found using techniques such as: deterministic annealing and genetic algorithms Weakness Applicable only when mean is defined, then what about categorical data? Need to specify k, the number of clusters, in advance Unable to handle noisy data and outliers Not suitable to discover clusters with non-convex shapes May 22, 2017 Data Mining: Concepts and Techniques 14 Cluster analysis groups objects based on their similarity and has wide applications Measure of similarity can be computed for various types of data Clustering algorithms can be categorized into partitioning methods, hierarchical methods, density-based methods, gridbased methods, and model-based methods Outlier detection and analysis are very useful for fraud detection, etc. and can be performed by statistical, distancebased or deviation-based approaches There are still lots of research issues on cluster analysis May 22, 2017 Data Mining: Concepts and Techniques 15