Geodatabases

Geodatabases

Geodatabasesby Shawn J. Dorsch

Spatial Databases Part 2

TopicsDefinitionsSpatial Database vs. GeodatabaseReference SystemsTypes of DataSpatial Query Processing

DefinitionsSpatial Database a database that models space, objects in space, or a combination of both. (Reainthong 3)

Geodatabase a specialized spatial database that deals specifically with geographical data.

Whats the difference? A spatial database is used to store a model of any objects within a space.Might store the components and layout of a circuit boardA geodatabase will hold data within the reference of the world.Coordinates of a city, boundary of a state, or shape of a river

Spatial Reference SystemA projection of the real world into a dataset that defines how spatial data is related.World Geodetic System (WGS84) one of the most used geographical reference systems.The Earth is a sphere so it cannot be projected with 100% accuracy.http://spatialreference.org/

GIS and Geodatabases GIS is software that allows the data to be visualized and analyzed.Search, perform calculations, analyze results, and view statisticsGeodatabases are one means by which GIS can store and query the data.Also flat data files or geo-raster files.

Types of DataTraditional dataNon-geographical dataFeature dataData stored as points, lines, and areasRaster dataImagery data that is geo-rectified.

Traditional DataIDAddrCityStateZip1123 Main St.SpringfieldIL506412554 Fake St.CressonPA15963313 Cherry Ln.AltoonaPA15904Can be stored using a traditional DBMSProcessed with standard SQL

Feature DataIDAddrCityStateZipLocation1123 Main St.SpringfieldIL50641

2554 Fake St.CressonPA15963

313 Cherry Ln.AltoonaPA15904

An object that stores a geographical representationUses vector geometryGood for objects with discrete boundariesStreets, rivers, lakes, states

Feature Datatypes

- (Shekhar and Sanjay 12)

Raster DataImagery dataSatellite imagery, Weather mapsBitmaps, PNGs, JPEGs

How do we query a bitmap?Need to store geographical reference dataThe coordinate systemA reference point or x,y coordinatetypically the upper left or the lower left corner of the rasterA cell sizeThe count of rows and columns

How do we query a bitmap?

- (shown in ArcGIS Desktop Help)

Storage of RastersCellShapeImageCorner1

1.jpg

Flat file uses process called geotaggingAdd spatial reference as metadataStore them in a geodatabase2 methods:Store reference to the image file

Store image in the tableCellShapeImageCorner1

Spatial QueriesTraditional queryFind all the stores that sell books on databases.Spatial queryFind all the stores that sell books on databases within 10 miles of zip code 15931.

Spatial OperatorsDistanceEqualsDisjointIntersectsTouchesCrossesOverlapsContainsIntersectsLengthArea

Query ProcessingIDStoreNameLocation1Store 1

Single stage query: each tuple has to be accessed at most once.Find all the stores within 10 miles of zip code 15931.

ZipLocation15931

spatial queryStoresZips

Query ProcessingMulti stage query: The tuples are sent thru a series of filter queries where each one reduces the size of the result set.Each filter get increasingly more complex and more costly.

- (shown in Spatial Concepts)

Query ProcessingIDNameAddrLocation1John Doe123 Main St

Find all store owners who live within ten miles of their store.IDNameOwnerIDLocation100Books R Us1

PeopleStores1st Stage2nd Stage

IndexingR-Trees like a B-tree, but for multi dimensional dataSplits data into a set of minimum bounding rectanglesAt each level of the tree the rectangles get smallerQuad-Trees tree structure, internal nodes have up to 4 childrenRegions are recursively split into 4 quadrants that get smaller and smaller

SummaryGeodatabases are a type of spatial databaseData is only meaningful in the context of a reference systemThree types of dataTraditional, feature, and rasterSDBMS runs queries in stages to increase efficiency

BibliographyShekhar, Shashi and Chawla, Sanjay. Spatial Databases A Tour. Prentice Hall, 2003 Shekhar, Shashi and Chawla, Sanjay. Chapter 2: Spatial Concepts and Data Models. Slides for Spatial Databases: A Tour. Nov. 27, 2009 . Gting, Ralf Hartmut. An Introduction to Spatial Database Systems. dna.fernuni-hagen. Sept. 1994. Nov. 27, 2009 .Welcome to ArcGIS Desktop Help 9.2. ArcGIS Desktop Help 9.2. March 15, 2007. Nov. 27, 2009 .Object Modeling and Geodatabases. University of Texas at Austin Center for Research in Water Resources. July 23, 1995. Nov. 27, 2009 .Spatial Concepts. Oracle Spatial User's Guide and Reference. Nov. 27, 2009 . Reainthong, Tyler. Spatial Database Systems. CSE 5330/7330 Fall 2009 FILE ORGANIZATION AND DATABASE MANAGEMENT. Nov. 27, 2009 .

Questions?Email me at: [email protected]