What is Where?
A GIS can answer the question: What is where? • WHAT: Characteristics of attributes or features. • WHERE: In geographic space.
A GIS links attribute and spatial data • Attribute Data • Flat File • Relations • Map Data • Point File • Line File • Area File • Topology • Theme
Distinguishing Characteristics of a GIS vs. Other Systems • provides links to ATTRIBUTES of points, lines, areas, grids in a database • provides algorithms for ANALYSIS of spatial data • “spatially intelligent” - “thinks” points, lines, areas, grids are actual spots on earth’s surface - e.g., switching projections, computing distances
What is a Data Model? • A logical construct for the storage and retrieval of information. • GIS map data structures are needed for map data models. • Attribute data models are needed for the DBMS. • The origin of DBMS data models is in computer science.
A DBMS contains: • Data definition language • Data dictionary • Data-entry module • Data update module • Report generator • Query language
GIS and DBMS • Geographic search is the secret to GIS data retrieval. • Many forms of data organization are incapable of geographic search. • GI systems have embedded DBMSs, or link to a commercial DBMS. • Examples: Dbase, ORACLE, Excel, Paradox
Database Structures: • Flat file • Hierarchical • Network • Relational • Object Oriented
Database structure -Flat file A flat file contains all data in a large table, with rows and columns ID Name Stat e Populatio n Are a Type 1 Whitefish Bay WI … … … 5 Shorewood WI … … … 6 Bayside WI … … … 9 Glendale WI … … … 12 Grafton WI … … … 14 Brown Deer WI … … … 18 Chicago IL … … … 7 records, each record contains 6 fields
Historically, databases were structured hierarchically in files... USA California Oregon New York Santa Barbara Ventura Contra Costa
Hierarchical systems • Hierarchical systems have a parent/child relation, are easy to understand, update and expand. • Direct correlation between one branch and another. • Based on formal criteria or key descriptors. • Work well if the structure of all possible queries is known beforehand
• Rigid structure • Needs lots of index files • Creates large files • If criterion or key descriptor information is incomplete, search is severely hampered. Hierarchical properties
Most current GIS DBM is by relational databases. • Based on multiple flat files for records • Dissimilar attribute structures • Connected by a common key attribute. • Key is a UNIQUE identifier at the “atomic” level for every record.
Relational Data Bases Purchase Record Item Date Price Customer Key Skate Board 2/1/96 49.95 John Smith 42 Baseball Bat 2/1/96 17.99 James Brown 978 Patient Record Key Check-in Check Out Room No.
- Summer '18
- Cartography, Geographic information system