Lecture 10 Creating and Maintaining

Geographic Databases

Longley et al., Ch. 10, through section 10.4

Outline

DefinitionsCharacteristics of DBMSTypes of databasesRelational modelSQLQueries as a gateway to spatial analysis

cell towers+/- 500 mGoogle db of

tower locations

Graphic courtesy of Wired, Feb. 2009

Wi-Fi+/- 30 mSkyhook

servers and dbiPhone GPS+/- 10 m

iPhone uses reference network

Definitions

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

A GIS can answer the question: What is where?

WHAT: Characteristics of features (= attributes).WHERE: In geographic space.

A GIS links attribute and spatial data

Attribute Data• Flat File or

DBMS• Relationships• Topology Table

Map Data• Point File• Line File• Area File• Topology Type

Flat File or DBMS

Record Value Value Value

Attribute Attribute Attribute

Record Value Value Value

Record Value Value Value

Ancient DBMS

From Clarke, Getting Started with GIS

Types of DBMS Models

HierarchicalNetworkRelational - RDBMSObject-oriented - OODBMSObject-relational - ORDBMS

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

Relational Databases rule now

Characteristics of DBMS (1)

Support for multiple data typese.g MS Access: Text, Memo, Number, Date/Time, Currency, AutoNumber, Yes/No, OLE Object, Hyperlink, Lookup Wizard

Load data from files, databases and other applicationsIndex for rapid retrieval

Characteristics of DBMS (2)

Query language – e.g., SQLSecurity – controlled access to data

Multi-level groups

Controlled update using a transaction managerBackup and recovery

Characteristics of DBMS (3)

ApplicationsForms builderReportwriterInternet Application ServerCASE tools

Programmable API

Geographic Information

System

Database Management

System

• Data loading• Editing• Visualization• Mapping• Analysis

• Storage• Indexing• Security• Query

Data

System TaskRole of DBMS

Relational DBMS (1)

Data stored as tuples (tup-el), conceptualized as tablesTable – data about a class of objects

Two-dimensional list (array)Rows = objectsColumns = object states (properties, attributes)

Table

Row = objectVector feature

Column = attribute

Relational DBMS (2)

Most popular type of DBMSOver 95% of data in DBMS is in RDBMS

Commercial systemsIBM DB2InformixMicrosoft AccessMicrosoft SQL ServerOracleSybase

Relational Join

Fundamental query operationOccurs 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

Relational Databases

SQL

Structured (Standard) Query Language – (pronounced SEQUEL)Developed by IBM in 1970sNow de facto and de jure standard for accessing relational databasesThree types of usage

Stand alone queriesHigh level programmingEmbedded in other applications

Types of SQL Statements

Data Definition Language (DDL)Create, alter and delete dataCREATE TABLE, CREATE INDEX

Data Manipulation Language (DML)Retrieve and manipulate dataSELECT, UPDATE, DELETE, INSERT

Data Control Languages (DCL)Control security of dataGRANT, CREATE USER, DROP USER

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.

Overlay

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

Overlay

01

Overlay like an attribute join

Types of overlay operations

UnionIntersectIdentityMaxMin

Etc.

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

Union

within 25 miles of a city OR within

25 miles of a major river.

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

Intersect

within 25 miles of a city AND within

25 miles of a major river.

Identitycomputes 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.

Identity

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.

Portion of the major city buffer WITHIN the major river buffer

Identity

Intersect

Buffer

Complex Retrieval: Map AlgebraCombinations of spatial and attribute queries

can build some complex and powerful GIS operations, such as weighting.

Weighted overlay analysis really just complex

retrieval.

Map

Alg

ebra

Map A

lgebra

Comparedwith

RAINFALL 1990 RAINFALL 1991 MAX RAINFALL 1990-’91

RecodeOR

A-B = AGRICULTURAL

C-E = NON-AGRICULTURAL