1. Lecture 08 Creating a Geodatabase
GTECH 361
Lecture 08 Creating 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 Geodatabase models
All relationships between features
Can take months in a big project
Geodatabase models

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
Parametric curves

5. Z and M Values Z values M 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