Fundamental GIS Database Concepts

ContentsThe GIS Database

Graphic DataSymbologyAnnotation

LayersNongraphic Data

TopologyData ManagementBasic Data Models

TablesSQL

Data DirectoryDatabase Administration

Distributed GISSummary

References

The GIS Database

Definitions

Database – an integrated set of data on a particular subject

Geographic (=spatial) database - database containing geographic data of a particular subject for a particular area

Database Management System (DBMS) – software to create, maintain and access databases

Advantages of Databases over Files

Avoids redundancy and duplication

Reduces data maintenance costs

Applications are separated from the data

Applications persist over time

Support multiple concurrent applications

Better data sharing

Security and standards can be defined and enforce

Disadvantages of Databases over Files

Expense

Complexity

Performance – especially complex data types

Integration with other systems can be difficult

Characteristics of DBMS (from Longley)

Data model 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

Query language – SQL

Security – controlled access to data

Multi-level groups

Controlled update using a transaction manager

Backup and recovery

DBA tools

Configuration, tuning

Applications

CASE tools

Forms builder

Reportwriter

Internet Application Server

Programmable API

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A GIS database can be divided into two basic types of data: graphic and nongraphic. Each of these types has specific characteristics, and each as different requirements for efficient data storage, processing and display.

Graphic DataGraphic data are digital descriptions of map features. They may include the coordinates, rules, and symbols that define specific cartographic elements on a map.

The GIS uses graphic data to generate a map or cartographic picture on a display, paper, or other media

6 Types of Graphic Elements

1. PointsZero-dimensional object that specifies a geometric location through a set of coordinates. A node is a special type of point that is a topological junction or end point and may specify a geometric location.

2. LinesA line is a one-dimensional object. A line segment is a direct line between two points. Special forms of lines include strings, arcs, and chains.

3. AreasAre bounded, continuous two-dimensional objects that may or may not include its boundary. Individual areas are represented as polygons.

Image -Copyright © 2000, Urban and Regional Information Systems Association

4. Grid cellsAre two-dimensional objects that represent a single element of a continuous surface.Raster point data is represented by a single cell. Line data is represented by a series of neighboring cells and areas by groups of contiguous cells.

5. PixelsA two-dimensional picture element that is the smallest indivisible element of an image

6. SymbolsGraphic elements that represent features at points on a mapAbstract geometric shapes can be used to represent real world features Computer graphics have facilitated the use of more complex and meaningful symbols

Building Road Tree

Grid Cell

Pixel

.

j l e l x q h y b d q n k y t r x p w h

GIS is equipped to display a wide variety of symbols for points, lines, and areas.

Symbols are frequently constructed and stored in system libraries, reflecting traditional cartographic representations or custom graphics

Check out the site on-line, created by users of ESRI products. The site is a resource for more symbol sets, downloadable for free.

The Unofficial Arc/Info and ArcView Symbol Page

This is a point symbol palette from ArcViewArcView also provides extensive line symbols to represent linear features such as rivers, roads, and railroads.

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AnnotationThe text or labels plotted graphically on a map and includes such items as street names, place names, identification numbers, and dimensions.

Usually not stored like other map features in GIS. It is not stored as strings of coordinates but often rather as a combination of location coordinates, standard fonts, and placement or orientation rules.

Three other items of information are stored for annotationLocation Orientation SizeAnnotation is the alphanumeric text or labeling placed on maps.

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Layers

Sample FontsTimes Roman

CursiveCarlson

Arial BlackBook Antiqua

CastellarGaramond

The

graphic component of the GIS database is often described as a series of layers, each of which contains map features that are related functionally.Each layer is a set of homogeneous features that is registered positionally to the other data base layers through the common coordinate system. The electronic layering scheme is comparable to a series of overlays in a manual mapping system.The sequence of layers usually begins with the reference grid or base features.The concept of data organization in layers is useful for communicating data structure

Image -Copyright © 2000, Urban and Regional Information Systems Association

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Nongraphic Data

Nongraphic data are representations of the characteristics, qualities, or relationships of map features and geographic locationsThey are stored in standard alphanumeric formatOften called textual data or attributesThey are related to geographic locations or graphic elements and are linked to them in the GIS through common identifiers or other mechanisms.Provide descriptive information about the characteristics of map features.

Four Classes of Nongraphic Data

1. Nongraphic AttributesDescribe in words and numerals the entities represented by the graphic elementsCan include qualitative and quantitative data that describe a point, line, polygon, or network feature stored in the database.A GIS is able to query or analyze the attributes separately and to generate a map based on nongraphic values, for example, all sites with gold crowns in them.Describe the map featuresLinked to graphic elements through identifiers or geocodes

2. Geographically Referenced DataDescribe physical phenomena, human-made features, and events that occur at a specific geographic locationStored and managed in separate files and systems that are not directly associated with the graphic features in a GIS database.They do contain elements that identify the location of the event of phenomenon. Building permits through street addresses, for example.Describe items or actions at a geographic location.They DO NOT describe the map feature

Examples: building permits, accident reports, health inspections

3. Geographic Indexes

Help locate map features and data based on their geographic identifiersAn index may include multiple identifiers for entities used by different organizations as well as listings of geocodes that identify the spatial relationships between locations or between features and geographic entities.Used to locate rows quicklyRDBMS use simple 1-d indexing (R-tree, B-tree, etc.)Spatial DBMS need 2-d, hierarchical indexing

1 2

SPATIALR ELATIO N SH IPS

C onnec tiv ity A d jacency P roxim ity

GridQuadtreeR-treeOthers

Multi-level queries often used for performance (MBR)Used to select, relate, and retrieve spatial dataExample: street address, mailing address, parcel number, account number

4. Spatial Relationships

Descriptions of the

proximity, adjacency, and connectivity of map featuresWhere things are located in proximity to each otherSome relationships also can be interpreted or calculated form the geographic coordinates of graphic elements- for example, number of arch sites within a five-mile radius of a natural spring.Topological relationships

example: nodes terminated at a specific linkexample: interpreted or calculated relationships

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Topology

The relative location of geographic phenomena independent of their exact position. In digital data, topological relationships such as connectivity, adjacency and relative position are usually expressed as relationships between nodes, links and polygons. For example, the topology of a line includes its from- and to-nodes, and its left and right polygons. Topology is useful in GIS because many spatial modeling operations don't require co-ordinates, only topological information. For example, to find an optimal path between two points requires a list of the lines or arcs that connect to each other and the cost to traverse each line in each direction. Co-ordinates are only needed for drawing the path after it is calculated.

(Copyright © 1999, Association for Geographic Information)

Topology a technique used to record and manipulate the logical relationships of map features and geologic information in a GISUsed in editing and quality control and retrieval and analytical functions

ArcUser Article on Topology and Shapefiles

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Data ManagementSince the storage structures can be tailored to the characteristics of the various data types, a GIS could have a graphic structure for coordinates, a topological structure for spatial relationships, and a conventional data base management system for attributes.Graphic data - high volume, requires efficient find and retrieval proceduresNon graphic data generally can use standard alphanumeric data management software and structures

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Basic Data Models

Hierarchicalparent-child relationshipsone-to-many relationshipsefficient for “standard” or predefined queries

“Computer database structures employing parent child or one-to-many relationship that requires direct linkages among items for a search to be successful” (2005 DeMers).

Sequential or Flat File

Not a true database management systemFiles managed by specifically developed systems or programs in COBAL, BASIC or other languagesTailored to individual applicationsOrdered based on some form of alphanumeric scheme

much more like alphabetizing a mailing list. This file structure makes it more difficult for data input, but allows searches and retrieval with greater speed than with simple lists.

RelationalBased on matrix structure of rows and columns of data

Facilitates ad-hoc queriesAssumes non-standard inquiriesMost popular choice for GIS“Big” vendors include: Oracle, Sybase, Ingres, Microsoft AccessData stored as tuples (tup-el), conceptualized as tablesTable – data about a class of objects

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

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

Commercial systemsIBM DB2InformixMicrosoft AccessMicrosoft SQL ServerOracleSybase

“Computer database structures employing an ordered set of attribute values or records known as tuples grouped into two-dimensional tables called relations” (2005 DeMers).

Object-Oriented

Object-oriented – OODBMS“GIS systems based on object-oriented programming methods and demonstrating object inheritance” (2005 DeMers).

NetworkCan model one-to many or many-to-many relationships

Records of the same type are grouped into conceptual filesUnlike hierarchical data structures, network systems are not restricted to paths up and down hierarchical pathways“Computer database structures employing a series of software pointers from one data item to

another. Unlike hierarchical data structures, network systems are not restricted to paths up and down hierarchical pathways” (2005 DeMers).

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TablesA table lets you work with data from a tabular data source in ArcGIS. You can bring data from almost any tabular data source in your organization into ArcGIS as tables. Then you can add data from these tables to maps, and symbolize, query and analyze this data geographically.

Table – data about a class of objectsTwo-dimensional list (array)Rows = objectsColumns = object states (properties, attributes)

Row = objectColumn = property

Table = Object Class

Object Classes withGeometry called Feature Classes

Sources of Tabular Data in ArcViewdbase, INFO, and delimited text filesSQL database serversFrom ArcMap, you can connect to a database server, such as Oracle or Sybase, and run an SQL to retrieve records from it as a table. ArcMap stores the definition of the SQL query you used, not the records themselves. See Connecting to a database to create a table

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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 queries High level programming

Embedded in other applications

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

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Data Directorya.k.a. Database Design or Database DictionaryA data dictionary is essential to effective management of database. It defines entities, attributes and valid values.The data dictionary also includes information that describes accuracy, completeness, vintage, or other data characteristics.

Review this example of a data dictionary: Data Dictionary

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Database AdministrationProtect database integrityMaintain data directory or database designControl passwords and access to databaseEstablish data standards, definitions, quality, and maintenance schedulesBackup and copy data

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Distributed GIS

Maintain data directory or database designControl passwords and access to databaseEstablish data standards, definitions, quality, and maintenance schedules TThe component parts can be at different locations

The userThe dataThe software

The network links all of the parts together

The Subject LocationAlso important to GIS is the area that is the subject of the GIS project

In principle a subject area can be studied by a GIS user located anywhere on the Earth's surfaceThe power of GIS is greatly enhanced when the user is located in the subject location

Information from the database can then be combined with information from the user's senses

The Role of StandardsDistributed GIS relies on the adoption of common standards

To allow the various components to operate togetherSuch standards have been developed by various national and international bodies, aided by the Open Geospatial Consortium

Distributing the DataIt must be possible to find remotely located data

Data documentation, or metadata, provides the key to successful searchThe U.S. Federal Geographic Data Committee devised a much-emulated standard for geographic data description

The Content Standard for Digital Geospatial Metadata

Geolibraries and Geoportals

A Geolibrary is a digital library containing georeferenced information

Its search mechanism uses geographic location as the primary key

www.alexandria.ucsb.edu

A Geoportal is a digital library of geographic data and GIServices

A one-stop shop for information relevant to GIS

www.geo-one-stop.gov

The Mobile UserIt is increasingly possible to obtain the services of a GIS through hand-held and wearable devices

Some cell phones can now be used to generate mapsSuch maps can be centered on the user's current location

http://www.garmin.com/pressroom/corporate/090805.html

Virtual RealityUse of digital technology to create an artificial visual and auditory environment that simulates the actual environment elsewhere

User and subject are in different locationsTechnology allows the user to explore a remote location

www.casa.ucl.ac.uk/research/virtuallondon.htmand

www.cvrlab.org

Augmented RealityThe user is in the subject location

Technology is used to augment the user's sensesInformation from a database can be displayed directly in the user's field of view

Superimposed on what is actually seen

Distributing the SoftwareA GIService is a GIS process provided remotely

A user can send a request and receive a resultA gazetteer service will accept a placename and return that location's coordinatesA geocoding service will accept a street address and return the house's coordinates

Advantages of GIServicesUsers do not need to obtain and install expensive softwareOnly one version of the service software need exist

It is always the latest versionData used in the service can be kept constantly up to date

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Summary

Database – an integrated set of data on a particular subjectDatabases offer many advantages over filesRelational databases dominateSome limitations for GIS

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ReferencesAntenucci, John et. Al. Geographic Information Systems - A Guide to the Technology. New York: Van Nostrand Reinhold, 1991. Chapter 5: DataBase Concepts pp. 96-102.DeMers, M N. Fundamentals of Geographic Information Systems. (2005) John Wiley and Sons Ltd.Geographical Information Systems and Science. Longley PA, Goodchild MF, Maguire DJ, Rhind DW. (2001) John Wiley and Sons Ltd.Tutorial on GIS Database Concepts, A Free On-Line Publication Of Urban and Regional Information Systems Association, Prepared with the support of PlanGraphics, Inc.Foote, K. The Geographer's Craft, Department of Geography, University of Texas at Austin.Many of the sections in this web page were modified from the instructors slides developed for the Longley text.