Data Structures & GeoDatabase

Introduction

• You have been using GDBs from nearly the start of the course

• Why?• Because I think that most of the

time you will be using GDBs!• And…

Why?

• Because it is a convenient way to manage data– All types of data can be included– Features can be “smart”– Support of ArcGIS Data Models

• Because it provides an organizational structure that can represent real world features and behaviors (topology)

Know what?• How to create a GDB• How to create a FC• How to create a FDS• What you can put into a GDB• What you can put into a FC• What you can put into a FDS• And How you add it to these parts of a GDB

Flavors of GeoDatabases• File

– Small groups, one edit, fast, smaller– Collection of files– Stores ~1 terabyte of data– File folder

• Personal – Small groups, one edit, Access DB, one file– Storage limited to ~2 gigabytes– Microsoft Access DB (so mdb is extension)

• ArcSDE– SDE = Spatial Database Engine – Enterprise version– Large groups working with data, including editing– Usually on a Server

The Geodatabase• It is a single container for many

feature classes (FC) (layers, {themes} of any one feature geometry and geography

• Quite often the FCs are stored in Feature Datasets (FDS) • Data in a FDS can be topologically linked

• Topological links

• Annotation can be stored in the GDB

• Data files also

Gray!

Feature Class (FC)• Conceptual representation of a

category of geographic features.• Can include 1 or more point, line, &

area features– but only one of these geometry types– And must be of the same spatial

reference • Data has to be Loaded or Imported

Feature Dataset (FDS)

• A collection of feature classes that share the same spatial reference.

• It is because they share the same spatial reference that they can participate in topological relationships with each other.

• Several feature classes may be stored in the same feature dataset.

• Many kinds of features and objects (tables) can be included

The GDB itself

• Has no spatial reference• Is not fussy about what is put into

it• Features do not have to have the

same spatial reference – but must have one!

The possibilities…

From ESRI’s course Learning ArcGIS Desktop

IconsGDB

Feature Dataset

GDB table

Views of GDBCatalog View

WE view

Views of GDB

Catalog View

WE view

Annotation

Vector data: Network

Topologies

• Many datasets have features that could share boundaries or corners

• By creating a Topology you set up rules defining how features share their geometries.

• Editing a boundary or vertex shared by two or more features updates the shape of all of them.

Topologies

Geometric Networks• Some vector datasets need to support

connectivity tracing and network connectivity rules– Streams and rivers– Communications– Pipelines– Transportation (roads, railroads, canals)

• Geometric networks allow you to turn simple point and line features into network edge and junction features

Summary of data types

Name Range, length Applications

Short Integer

-32,768 to 32,767

No fractions

Long Integer

-2,147,483,648To2,147,483,647

No fractions

Float ~-34E-38 to ~1.2E38

Fractional values

Summary of data types

Name Range, length Applications

Double ~ -2.2E-308

~ 1.8E308

Fractions OK

Text <=64,000 char Names etc.

Date mm/dd/yy

hh:mm:ss

Date and time

Precision and Scale

• When creating new fields an attribute table You will be asked for these

• Precision: Describes the number of digits that can be stored in the field. All digits are counted no matter what side of the decimal they are on. But not the decimal point.

Scale

• Scale:Sets the number of decimal places stored in a field. Used in Float and Double data field types.

• If the input table is a personal or file GeoDatabase the field scale will be ignored.

• The number 1234.567 would have a precision of 7 and a scale of 3.

• The business of precision and scale is actually much more complicated than this

Planning

• What is the problem?• What data is needed (map scale,

extent, etc.?• What kinds of relationships are needed

between FC?• How will the data be organized (FDS)?