Lecture 10 Creating and Maintaining Geographic Databases

1. Longley et al., Ch. 10, through section 10.4 Lecture 10Creating and Maintaining Geographic Databases

2. Outline • Definitions • Characteristics of DBMS • Types of databases • Relational model • SQL • Queries as a gateway to spatial analysis

3. cell towers +/- 500 m Google db of tower locations Wi-Fi +/- 30 m Skyhook servers and db iPhone GPS +/- 10 m iPhone uses reference network Graphic courtesy of Wired, Feb. 2009

4. Definitions • Database – an integrated set of data (attributes) on a particular subject • Geographic (=geospatial) database - database containing geographic data of a particular subject for a particular area • Database Management System (DBMS) – software to create, maintain and access databases

5. A GIS can answer the question: What is where? • WHAT:Characteristics of features (= attributes). • WHERE:In geographic space.

6. Attribute Data Flat File or DBMS Relationships Topology Table Map Data Point File Line File Area File Topology Type A GIS links attribute and spatial data

7. Record Value Value Value Record Value Value Value Record Value Value Value Flat File or DBMS Attribute Attribute Attribute

8. Ancient DBMS From Clarke, Getting Started with GIS

9. Types of DBMS Models • Hierarchical • Network • Relational - RDBMS • Object-oriented - OODBMS • Object-relational - ORDBMS

10. Historically, databases were structured hierarchically in flat files...

11. Relational Databases rule now

12. Characteristics of DBMS (1) • Support for multiple data types • e.g MS Access: Text, Memo, Number, Date/Time, Currency, AutoNumber, Yes/No, OLE Object, Hyperlink, Lookup Wizard • Load data from files, databases and other applications • Index for rapid retrieval

13. Characteristics of DBMS (2) • Query language – e.g., SQL • Security – controlled access to data • Multi-level groups • Controlled update using a transaction manager • Backup and recovery

14. Characteristics of DBMS (3) • Applications • Forms builder • Reportwriter • Internet Application Server • CASE tools • Programmable API

15. Role of DBMS Task System • Data loading • Editing • Visualization • Mapping • Analysis Geographic Information System • Storage • Indexing • Security • Query Database Management System Data

16. Relational DBMS (1) • Data stored as tuples (tup-el), conceptualized as tables • Table – data about a class of objects • Two-dimensional list (array) • Rows = objects • Columns = object states (properties, attributes)

17. Table Column = attribute Row = object Vector feature

18. Relational DBMS (2) • Most popular type of DBMS • Over 95% of data in DBMS is in RDBMS • Commercial systems • IBM DB2 • Informix • Microsoft Access • Microsoft SQL Server • Oracle • Sybase

19. Relational Join • Fundamental query operation • Occurs because • Data created/maintained by different users, but integration needed for queries • Table joins use common keys (column values) • Table (attribute) join concept has been extended to geographic case

20. Relational Databases

21. SQL • Structured (Standard) Query Language – (pronounced SEQUEL) • Developed by IBM in 1970s • Now de facto and de jure standard for accessing relational databases • Three types of usage • Stand alone queries • High level programming • Embedded in other applications

22. Types of SQL Statements • Data Definition Language (DDL) • Create, alter and delete data • CREATE TABLE, CREATE INDEX • Data Manipulation Language (DML) • Retrieve and manipulate data • SELECT, UPDATE, DELETE, INSERT • Data Control Languages (DCL) • Control security of data • GRANT, CREATE USER, DROP USER

23. Spatial Search:Gateway to Spatial Analysis • Overlay is a spatial retrieval operation that is equivalent to an attribute join. • Buffering is a spatial retrieval around points, lines, or areas based on distance.

24. Image courtesy of K. Foote/M. Lynch, UT-Austin Overlay

26. Overlay 0 1

27. Overlay like an attribute join

28. Types of overlay operations • Union • Intersect • Identity • Max • Min Etc.

29. Union • computes the geometric intersection of two polygon coverages. All polygons from both coverages will be split at their intersections and preserved in the output coverage.

30. within 25 miles of a city OR within 25 miles of a major river. Union

31. Intersect • computes the geometric intersection of two coverages. Only those features in the area common to both coverages will be preserved in the output coverage.

32. Intersect within 25 miles of a city AND within 25 miles of a major river.

33. Identity • computes the geometric intersection of two coverages. All features of the input coverage, as well as those features of the identity coverage that overlap the input coverage, are preserved in the output coverage.

34. Identity Portion of the major city buffer WITHIN the major river buffer within 25 miles of a city OR within 25 miles of a major river. within 25 miles of a city AND within 25 miles of a major river.

35. Intersect Identity

36. Buffer

38. Complex Retrieval: Map Algebra Combinations of spatial and attribute queries can build some complex and powerful GIS operations, such as weighting. Weighted overlay analysis really just complex retrieval.

39. Map Algebra Map Algebra Compared with RAINFALL 1990 RAINFALL 1991 MAX RAINFALL 1990-’91

40. OR Recode

41. A-B = AGRICULTURAL C-E = NON-AGRICULTURAL