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Creating a Geodatabase: Organizing, Evaluating, and Modifying Data

This lecture covers organizing, evaluating, and defining the structure of geodatabases. Topics include spatial reference, modifying spatial domains, and precision considerations. Learn ways to define the geodatabase structure and add data efficiently. Explore supported field types and ways to modify Z and M domains. Understand coordinate systems, spatial extent, and precision values for optimal data storage.

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Creating a Geodatabase: Organizing, Evaluating, and Modifying Data

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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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