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Introduction to the Geodatabase. What is a Geodatabase? What are feature classes and feature...

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Introduction to the Geodatabase
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Introduction to the Geodatabase

• What is a Geodatabase?• What are feature classes and feature datasets?• What are domains• Design a personal Geodatabase• Import data to a Geodatabase

What is a Geodatabase?

• A container for tables, feature classes, feature datasets….• Tables – attributes of rows and columns• Standalone feature classes (conceptually like shape files)• Feature datasets (a collection of feature classes)• Rules and relationships

A relational database that contain geographic information

• Store geographic features represented as points, lines, or polygons, and their attributes;

• Can also store annotation and dimensions.

• Tables may contain additional attributes for a feature class

Feature classes…..

• Feature classes can be organized in Feature datasets.

• All feature classes in a feature dataset share the same coordinate system.

• Feature classes in a feature dataset can be organized into a geometric network. The network maintains topological relationships between its feature classes.

Feature datasets…..

Personal geodatabase - stores data in a Microsoft Access database

- size limit 2 GB- directly read through ArcCatalog- does not support raster data

Multiuser geodatabases - data stored in IBM DB2, Informix,

Oracle, or Microsoft SQL Server- connected through ArcSDE or direct- ArcSDE license necessary for editing- supports raster data

Personal vs. Multiuser Geodatabase

• All data (vector, raster, address, measures, CAD, etc.) is stored together in a commercial off-the-shelf DBMS

• Simplify support and maintenance, and reduce costs

• Allows multi-user access (with ArcSDE license)

• Support for intelligent features, rules, and relationships between feature classes

Why Geodatabase?

• Dynamic Geocoding

• Annotation subclasses

• Subtypes within Feature classes

• Coded attribute and range domains

• Improved topology and editing

More advantages…..

…however they are simply modern equivalents of shapefiles and coverages stored in a commercial database.

Confused?

-The geodatabase may seem complicated…..

- Geodatabases can be created and managed easily using the standard tools in ArcCatalog

- ArcMap and ArcToolbox provides tools to work with geodatabases

Geodatabases in ArcGIS

• Design process • Create an empty Geodatabase in ArcCatalog• Define the database structure• Set spatial reference and coordinate domains• Load data • Define topology rules and relationships

Creating a GeodatabaseThink before you create

Design process

• What data layers to include in the geodatabaseShape files – CoveragesLook-up tables

• How to organize the feature classes into logical feature datasets

• Think about what topolygy rules you may want to apply – how are the feature classes related to each other spatially?

Create a new Geodatabase in ArcCatalog

• Shape files and coverages are converted to feature classes

• Attributes can be left out or renamed

• CAD data, dBase files, annotation etc. can be imported

• Data of the same spatial extent can be imported to the same feature dataset

Migrating existing data into the Geodatabase

Importing existing data

• In ArcCatalog or ArcToolbox• Tools and wizards are available• Works with coverages, shapefiles, tables, CAD etc.

                 

                          

Creating Feature Datasets• Right-click on the geodatabase – New – Feature Dataset

• Name the Feature Dataset and define the coordinate system

• Set X/Y domain

• Set Z domain and M domain

• Set manually or import from existing data sets

Coordinate Domains

Lost data

Large areaSmaller precision (1,000)

Small area larger precision (100,000)

(0,0)

Y

X

Max X and Y is 2.14 billion

Coordinate Domains

• The coordinate domain defines the area you can make edits in

• X and Y max is 2.14 billion for the database

• Default domain is 21000, 21000

• Define your coordinate domains correctly the first time – they cannot be changed

• You can have a different coordinate domain for each feature class

What is max/min X and Y on the map?

Max X and Y

Min X and Y

Setting X/Y Domain Precision

Min X ~ 2,145,320Max X ~ 2,657,580Min Y ~ 1,632,610Max Y ~ 1,967,940

1 ft units, 1/1000 ft accuracyPrecision = 1000/1 = 1000 (good enough)

1000

(0,0)

Y

X

Max X and Y is 2.14 billion

Most of the data is here in the database Large expansion options to the north and east

Coordinate Domains

Coordinate Domains CalculationsMin X ~ 2,145,320Max X ~ 2,657,580Min Y ~ 1,632,610Max Y ~ 1,967,940Precision 1000

These coordinates would put the data in the lower left corner – however we want to shift this to be able to expand in all directions

(MinX + MaxX)/2 – (2.14 x 109) / (1000 x 2) = X min 2,401,450 – 1,070,000 = 1,331,450 (MinY + MaxY)/2 – (2.14 x 109) / (1000 x 2) = Y min 1,800,275 – 1,070,000 = 730,275

(MinX + MaxX)/2 + (2.14 x 109) / (1000 x 2) = X max 2,401,450 + 1,070,000 = 3,471,450 (MinY + MaxY)/2 + (2.14 x 109) / (1000 x 2) = Y max 1,800,275 + 1,070,000 = 2,870,275

Min X ~ 2,145,320Max X ~ 2,657,580Min Y ~ 1,632,610Max Y ~ 1,967,940Precision 1000

Min X = 1,331,450 Max X = 3,471,450 Min Y = 730,275Max Y = 2,870,275Precision 1000

Default x/y domain Shifted x/y domain

Coordinate Domains Calculations

(0,0)

Y

X

Max X and Y is 2.14 billion

Most of the data is here in the database Large expansion options in all directions

Coordinate Domains

The shifted x/y domain allows for editing within this window

Max X, Max Y

Min X, Min Y

Why create Feature Datsets?

• Data organization• Topology rules• Shared boundaries• Geometric networks

Subtypes in feature classesSubtypes can only be created in ArcEditor and ArcInfo

- A subtype is a group of objects that have similar properties within the Geodatabase

For example the attribute ‘ZoneCode’ may have subtypes:- Commercial, Residential, Industrial

Landcover vegetation types may have subtypes:- Forest, Agriculture, Rangeland, Urban

Attribute Domains

• Attribute domains are properties of the Geodatabase - Multiple objects may use the same domain - Can be created using the Domains properties dialog box

• Defines legal values for field attributes - Range domains (allowable numeric value range) - Coded value domain (in dropdown menus)

Questions?


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