Geodatabases by Shawn J. Dorsch

Spatial Databases Part 2

Topics Definitions Spatial Database vs. Geodatabase Reference Systems Types of Data Spatial Query Processing

Definitions Spatial 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.

What’s 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 board A 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 System A 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.

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

Types of Data Traditional data – Non-geographical data Feature data – Data stored as points, lines, and areas Raster data – Imagery data that is geo-rectified.

Traditional Data IDAddrCityStateZip 1123 Main St.SpringfieldIL Fake St.CressonPA Cherry Ln.AltoonaPA15904 Can be stored using a traditional DBMS Processed with standard SQL

Feature Data IDAddrCityStateZipLocation 1123 Main St.SpringfieldIL Fake St.CressonPA Cherry Ln.AltoonaPA15904 An object that stores a geographical representation Uses vector geometry Good for objects with discrete boundaries – Streets, rivers, lakes, states

Feature Datatypes - (Shekhar and Sanjay 12)

Raster Data Imagery data – Satellite imagery, Weather maps – Bitmaps, PNGs, JPEGs

How do we query a bitmap? Need to store geographical reference data – The coordinate system – A reference point or x,y coordinate typically the upper left or the lower left corner of the raster – A cell size – The count of rows and columns

How do we query a bitmap? - (shown in ArcGIS Desktop Help)

Storage of Rasters CellShapeImageCorner… 1 1.jpg … Flat file uses process called geotagging – Add spatial reference as metadata Store them in a geodatabase – 2 methods: Store reference to the image file Store image in the table CellShapeImageCorner… 1 …

Spatial Queries Traditional query – Find all the stores that sell books on databases. Spatial query – Find all the stores that sell books on databases within 10 miles of zip code

Spatial Operators Distance Equals Disjoint Intersects Touches Crosses Overlaps Contains Intersects Length Area

Query Processing IDStoreNameLocation 1Store 1 Single stage query: each tuple has to be accessed at most once. – Find all the stores within 10 miles of zip code ZipLocation spatial query Stores Zips

Query Processing Multi 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 Processing IDNameAddrLocation 1John Doe123 Main St… Find all store owners who live within ten miles of their store. IDNameOwnerIDLocation 100Books R Us1 People Stores 1st Stage2nd Stage

Indexing R-Trees – like a B-tree, but for multi dimensional data – Splits data into a set of minimum bounding rectangles – At each level of the tree the rectangles get smaller Quad-Trees – tree structure, internal nodes have up to 4 children – Regions are recursively split into 4 quadrants that get smaller and smaller

Summary Geodatabases are a type of spatial database Data is only meaningful in the context of a reference system Three types of data – Traditional, feature, and raster SDBMS runs queries in stages to increase efficiency

Bibliography Shekhar, 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, Güting, Ralf Hartmut. “An Introduction to Spatial Database Systems.” dna.fernuni-hagen. Sept Nov. 27, “Welcome to ArcGIS Desktop Help 9.2.“ ArcGIS Desktop Help 9.2. March 15, Nov. 27, “Object Modeling and Geodatabases.” University of Texas at Austin Center for Research in Water Resources. July 23, Nov. 27, “Spatial Concepts.” Oracle® Spatial User's Guide and Reference. Nov. 27, IHJF Reainthong, Tyler. “Spatial Database Systems.” CSE 5330/7330 Fall 2009 FILE ORGANIZATION AND DATABASE MANAGEMENT. Nov. 27,

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