Geog 495 Final Exam Review

11/23/05 Final exam on 11/28/05 Mon

I. Big picture – Attribute – Space – Attribute & Space

Outlines

II. Small picture – GIS view on spatial data – DBMS view on spatial data III. Synthesis

I. Big picture

• Geographic information has three main components: space, time, and attribute • Traditionally the representation of attribute is well studied in contrast to space and time • How attribute is represented in computer  half of this course) database model (first • How space is represented in computer  (second half of this course) spatial data model • How space is combined with attribute – In GIS (GIS Architecture) – In DBMS (SDBMS Architecture) – Integration of GIS with DBMS

Database model

• Hierarchical • Network • Relational • Object-oriented • Object-relational

Spatial data model

• Object view • Field view

GIS architecture

• Hybrid • Purely relational • Object-oriented or object-relational File-system into database system

SDBMS architecture

• Purely relational • Object-oriented • Object-relational Accommodated into spatial semantics

Integrating GIS with SDBMS

• GIS-centered – e.g. Arc/Info ODBC – What’s the relative advantage of this approach?

• SDBMS-centered – e.g. Oracle Spatial – What’s the relative advantage of this approach?

GIService

• Utilize specialized GIS functionalities that meet specific needs • Built upon DBMS • Somewhat eclectic: good things from both

II. Small picture

• Two views on spatial data model • GIS view: focused on how to store spatial information suited to application needs (e.g. building topology for routing applications) • SDBMS view: focused on how to store spatial information suited to SQL-like queries (e.g. defining spatial data type, spatial operators)

1. GIS view on spatial data

• Data hierarchy – Data model: how spatial concepts are viewed – Data structure: how spatial information in stored in computer – Data format: how data structure is stored in s/w specific format Human thinking Level of abstraction Machine code

Data model

• There are two common views • Object-view – The world is composed of discrete entities • Field-view – The world is composed of continuous fields • Both coexists in the real-world • One phenomenon can be represented in two views • Human perception tends to discretize information also

Data structure

• Data structure that stores spatial information – Vector: composed of (a set of) point – Raster: composed of grid cell • Data structure that stores attributes derived from spatial relationships – TIN: connected network of points whose attributes vary – Matrix: represent attributes based on a pair of spatial objects

Do you know?

• Vertice, node, point, line, polygon, multishape polygon, multistring….

• Topology vs. spaghetti model • Planar vs. non-planar • Compression methods for raster data structure – Run-length code – Quadtree

File format

• Different systems use different file formats • Needs for interoperability – How can we promote interoperability?

• Metadata – Metadata standard?

– What kind of information is documented?

– FGDC standard

Do you know?

• SDTS • XML • Open GIS • Characteristics of specific file format and how they are classified into different data model?

– TIGER/Line – DEM – MrSID, BIL, GeoTiff (These are common DOQ format)

2. DBMS view on spatial data

• Spatial data type • Spatial operators

Spatial data type

• Object – Point sets – Do you know OGIS spatial object types?

• Field – Tessellation (grid) representation – No too much work has been done

Spatial operators

• On field-based data – Local (e.g. +, -,…) – Focal (e.g. gradient) – Zonal (e.g. average) • On object-based data – Topological (e.g. within, overlap, touch) – Metric (e.g. distance, direction, area)

Miscellaneous

• What is spatial access method (or spatial indexing)?

– Quadtree vs. R tree • Query processing – Single scan vs. multi scan

III. Synthesis

• More DBMS approach to GIS is desirable – DB system is superior to file system – DB gets increasingly smarter – Distributed GIS environment gets increasingly popular

• Inadequacy of RDB to representing spatial concepts should be accommodated – User-defined spatial data types – User-defined spatial operators – Custom data model (refer to next week presentation on geodatabase case studies) – Geographer’s role for formalizing spatial concepts (Naïve geography?)