Lecture 08 Creating a Geodatabase 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 Geodatabase models All relationships between features Can take months in a big project Geodatabase models www.esri.com/software/arcgisdatamodels/

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

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

Supported Field Types

Supported Field Types

Ways to Define GDB Structure

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

Adding Data

Spatial Reference in the GDB

Coordinate Systems See session 03

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!

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

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

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

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

Defining z and m Domains

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)

Design Example

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