Organizing Geographic Data

Geographic data is recorded information about the earth's surface and the objects found on it, associated to a geographic location. Listed below are key points you should remember about geographic data.

	Two models for representing real-world features in a GIS are the vector data model and the raster data model.
	Geodatabases, shapefiles, and coverages are common file formats for storing vector data. Images and grids are common formats for raster data.
	There are three types of geodatabases: file geodatabases, personal geodatabases for Microsoft Access, and ArcSDE geodatabases that are used with relational database management systems and ArcSDE technology.
	Geodatabase feature classes can be stand-alone or they can be organized into larger units called feature datasets.
	The field type of an attribute determines the type of data that can be stored in it.
	Before you build a geodatabase, you need to spend time designing it.

Review questions

When would you use the vector data model versus the raster data model?
In a geodatabase polygon feature class, which two fields are automatically calculated and updated?
List three methods of adding data to a geodatabase.
If you wanted to combine features from different feature classes into one feature class, which method would you use?

Answers

If you want to represent features with distinct boundaries, it's probably better to use the vector data model and store the features' x,y coordinate locations. The raster data model is better suited to representing phenomena whose boundaries change gradually across a given area.
In a geodatabase polygon feature class, the Shape_Length and Shape_Area fields are automatically calculated and updated.
Three methods of adding data to a geodatabase are importing, loading, and copying data.
To combine features from different feature classes into one feature class, you would load them into a new, empty geodatabase feature class.

Key terms

	coverage
	data model
	feature class
	feature dataset
	geodatabase
	grid
	image
	raster
	shapefile
	thumbnail
	vector
	x,y coordinates