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GTECH 361

GTECH 361. Lecture 08 Creating a Geodatabase. Today’s Topics. Organizing data in a geodatabase Evaluating data Defining the geodatabase structure Adding data Understanding spatial reference Modifying the spatial domain. Organizing Data. Designing the geodatabase structure

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GTECH 361

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  1. GTECH 361 Lecture 08Creating a Geodatabase

  2. Today’s Topics • Organizing data in a geodatabase • Evaluating data • Defining the geodatabase structure • Adding data • Understanding spatial reference • Modifying the spatial domain

  3. Organizing Data • Designing the geodatabase structure • All relationships between features • Can take months in a big project • Geodatabase models • www.esri.com/software/arcgisdatamodels/

  4. Evaluating Your Data • Formats that can be migrated into a geodatabase: • CAD • Shapefile • Feature geometry types supported are: • Point • Line • Polygon • Coverage • dBASE • INFO tables • z values • m values • Parametriccurves

  5. Z and M Values • Z values • Store 3-D values for a vertex • 3-D shapefile • Draped feature class over a surface • M values • Store linear measures from a vertex

  6. Supported Field Types

  7. Supported Field Types

  8. Ways to Define GDB Structure

  9. Defining GDB Structure • Import existing data • Wizards and tools • Create structure manually • Wizards and tools in ArcCatalog to • Create new empty feature datasets, classes, and tables • Define attribute fields • CASE tools • UML tools like Visio or Rational Rose

  10. Adding Data

  11. Spatial Reference in the GDB

  12. Coordinate Systems • See session 03

  13. Spatial Extent • Allowable range for x and y coordinates • Typically max and min x, y values • When you start from scratch and define a coordinate system, you will also have to define an extent • When you import from another GDB feature class, the extent is inherited • When you import from a shapefile or coverage, the extent is a buffer around the features • Once a new feature class or feature dataset has been created, you cannot change its spatial extent!

  14. Precision • GDB coordinates are stored as integers • Precision is used to convert numbers with decimals to integers

  15. Spatial Domain • Precision and coordinate values together define the spatial domain • Increasing the precision value decreases the spatial extent • Decreasing the precision value increases it • As the precision value increases, so does the data resolution that can be stored in the GDB

  16. Modifying Spatial Domain • Pyung Ho’s bus network example • If you don't know how large a spatial extent your data will require, center your data in GDB coordinate space and explicitly define your precision

  17. Precision Considerations • Choose the smallest precision that allows for updates to your data and anticipates future growth, and that supports the highest level of accuracy required for the data • An inappropriate precision can affect the cluster tolerance for a topology. As the precision increases, the possible maximum cluster tolerance decreases

  18. Defining z and m Domains

  19. Modifying z and m Domains • z and m values adhere to the same rules as x, y values • Range and precision apply just the same • An application for changing z domain is for example if you work with land areas beneath sea level ( < 0)

  20. Design Example

  21. Design Example, part 2 • Defining GDB from scratch, then importing legacy data • Selecting appropriate coordinate system • Reviewing default spatial domain generated by ArcGIS • Adjust spatial domain • Determining scale of data collection and accuracy requirements

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