Geog 495 Final Exam Review 11/23/05 Final exam on 11/28/05 Mon

Outlines I. Big picture –Attribute –Space –Attribute & Space 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  database model (first half of this course) How space is represented in computer  spatial data model (second half of this course) 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 Level of abstraction Human thinking 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?)