GED 554

GED 554
Topology (for geometry)
Working with Data Tables, Databases (for attributes)
April 12, 2013
Supported Data Types
• ArcGIS supports three representations of geographic data.
– Vector data for representing features
– Raster data for images
– Tabular data
Spatial and attribute data form a geographic database…
Features can be categorized into three basic classes…
points
lines
polygons
Geographic Feature Data Formats
•
Shapefile – introduced with ArcView (old version)
– non-topological vector data format.
– much GIS data in Shapefile format.
– limited analysis capabilities due to lack of topology
•
Geodatabase – introduced in ArcInfo 8
– Object-oriented model – can characterize features more naturally by
defining object types, topological, spatial and general relationships, and
interactions.
– Geodatabase features can be stored in a single database.
– Create custom features in addition to points, lines, polygons
– Brings physical model closer to logical model.
Shapefile
• Single feature class -can only contain one feature class
• Attributes stored in dBASE table: *.dbf e.g. soils.dbf
• Each shapefile consists of at least three files: *.shp, *.shx,and
*.dbf.
• If the shapefile has a defined coordinate system then the
spatial reference information will be stored in a *.prj file
• In addition to the above four files other files may be created
and/or used by ArcGIS as needed
Personel Geodatabase (single user)
• Implemented as a Microsoft Access database (*.mdb
file) by using MS jet engine which is installed with
ArcGIS. MS access is not needed.
• Can contain multiple feature classes
• Generally used for personal or small work-group use.
• Can handle small to moderately sized datasets (max.
size is 2.0 GB)
• Supports topology
Feature Class
Group objects into homogeneous types
Create point, line, or area feature classes
A collection of geographic objects with the same geometry (point, line, polygon)
that share the same attributes.
Feature Dataset
• must have same coordinate system
• should group feature classes based on
topology
Feature
Feature Class
Road
Lines
Boundaries
Polygons
Pole
Points
Label & Text
Annotation
Feature Dataset
Set of feature classes
that share the same
spatial reference
Linking Features and Attributes
• Feature classes have an associated table
• Each feature has a record in the table
• A unique identifier links feature and attributes
ArcCatalog is the Principal User
Interface Used to Define
and Manage the
Geodatabase
Relationship
between
geometries
Topology is the arrangement that defines how point, line, and polygon features
share coincident geometry.
Topology
• Topology rules define the permissible spatial relationships
between features.
• For example, the rule Must not overlap is used to manage the
integrity of features in the same feature class. If two features
overlap, the overlapping geometries are displayed in red (such
as shown by the overlapping red area in the adjacent
polygons and the linear segment of the two lines below).
•Parcels cannot overlap. Adjacent parcels have
shared boundaries.
•Stream lines cannot overlap and must connect to
one another at their endpoints.
•Adjacent counties have shared edges. Counties
must completely cover cities.
•Road centerlines must connect at their
endpoints.
Why do we need topology in GIS?
• Enforce geometric rules for spatial
representation and maintain data integrity
• Reduce data redundancy
• Improve data access/update efficiency
GIS=Lots of Tabular Data
Working with tabular data
• Table Structure
– Records/rows and fields/columns
– Columns can store number, text or date data types
– User able to assign column names for additional
attributes
Fields are defined:
• Name –attribute (column heading)
• Field Type –number (long, short, float, double), text
(“string”), or date
• Length –no. of characters in text
• Precision –no. of digits used to store numbers
• Scale –no. of digits to right of decimal point
Fields types in ArcGIS
Associating Tables to Feature Classes
• Can store attributes in feature table or separate table
• Associate tables with common column key values
– Primary keys have unique values
– Primary keys can exist as Foreign keys in other tables
When working with data tables
• Goals:
– Maximize flexibility for sorting, searching
– Efficient storage; eliminate redundancy
– Secure entry mechanisms
– Rapid retrieval
• Solution:
– Database Management System (DBMS)
A database is an organized collection of data.
A database model is a type of data model that determines the
logical structure of a database and fundamentally determines in
which manner data can be stored, organized, and manipulated.
The most popular example of a database model is the relational
model, which uses a table-based format.
F: Two-dimensional array of
data elements
H: Tree-like structure
N: Many-to-many
relationships in a tree-like
structure
R: Multiple tables which have
“key” identifiers to combine
data
OO:A particular application
can be defined directly in the
database
A DBMS provides:
• Accuracy -reduce errors during entry by use of
established rules, templates
• Efficiency-rapid access & retrieval, no
redundancy
GIS attribute data models
• Hierarchical–pre-1980
• Relational–1980’s, 1990’s; still dominant today
• Object-oriented–late ’90’s; newest, still
undergoing R&D
Hierarchical Structure
• File address for storage and retrieval is a linear
path, e.g.
C:\ESRI\ESRIDATA\CANADA\cities.shp
Relational Database Structure
• Consists of “relations” (tables) with multiple
attributes (columns) per record
• Every record (row) has a unique identifier
(marker or key attribute)
– Key is the glue between files that can be used to
extract and/or assemble records and attributes
Relational Database advantages
• Data stored in separate files
– Easy update, editing, searching without affecting
or using all data
• Flexibility
– Using key(s), can extract and assemble records
and attributes to form new tables
– Subsets of database can be queried by standard
means -SQL
SQL
• The most common query language used with
the relational model is the Structured Query
Language (SQL)
• A special-purpose programming language
designed for managing data held in a
relational database management systems
(RDBMS)
Operator
Description
=
Equal
<> or !=
Not equal
>
Greater than
<
Less than
>=
Greater than or equal
<=
Less than or equal
BETWEEN
Between an inclusive range
LIKE
Search for a pattern
IN
To specify multiple possible
values for a column
Relational Database Structure:
Properties of Relations
•
•
•
How many “A”objects are related to “B”objects
Four types of cardinality
– One-One
– One-Many
– Many-Many
– Many-One
User must know cardinality before connecting tables
Table Association and Table Join
• Table association
– Attributes about a feature can be stored
• Feature class table (Feature class)
• Separate table (Object class)
– Associate tables with common column (key) values
• Primary keys: Common field on original table
• Foreign keys: Common field on destination table
• Table join
– Merge two tables together into one table logically or physically (in ArcMap).
GISC 6382 Applied GIS UT-Dallas Briggs
33
Connecting Tables with Joins
•
•
•
•
Appears as a physical merging of two tables
Works with one-to-one or many-to-one relationships
Can be created either in ArcMap or ArcToolbox
Edits can only be made to the columns of the destination table –to edit
columns in the source or joined table, you must add it as it’s own data
table to the ArcMap session
Connecting Tables with Relationship Classes
• Tables are virtually linked, not physically connected
• Strengths:
– No new feature class created
– Once created the connection is active until removed
– Dynamic association -can see changes to parent tables
– Can edit, query, & symbolize the data in either table
– User has more flexible cardinality associations available
• Define the link in ArcCatalog
• Use the relationship in ArcMap
Geodatabase Elements
• Objects & Object classes
• Features & Feature classes
• Feature datasets
• Spatial references
• Domains
• Subtypes
• Relationships & Relationship classes
• Geometric networks
• Labels and Annotation
Objects & Object Classes
• Geodatabases organize geographic data into a hierarchy of data objects.
• Objects are instances of an object class that have properties and
behavior.
• Objects can be related to other objects via relationships
• Objects have unique system identifiers (OID)
• Object classes are tables in a geodatabase storing non-spatial data (e.g.,
Parcel owners)
• Objects in an object class have the same
– Properties - stored in the table as attributes
– Behavior - implemented as a component
A row stores an Object
Object Classes (tables)
Pump Table
OID
175
Pump Type
Axial Flow
Inlet Size
24”
…….
…….
…
…………
…………
…….
Features and Feature Classes
• Features are objects with required shape (Points, Multipoints, Lines & Polygons) that represent a real world object in
a layer on a map.
• Features classes are collections of features with same type of
feature geometry and attributes.
• A feature class is also an object class which stores spatial
objects (features) (e.g., Parcels).
• All the features in a feature class are in the same spatial
reference.
• Feature classes which store topological features must be
contained within a feature dataset to ensure a common
spatial reference.
Feature Classes
A row stores feature
Feature Class Table
Lateral Water Lines
OID
583
…
Shape
X,Y,Z,M
(BLOB)
…………
Type
Domestic
…….
…….
…………
…….
BLOB: Binary Large Object Block
Feature Datasets
• Containers for feature
classes
• Shared spatial reference
• May also contain
– relationship classes
– geometric networks
– Annotations
Annotation is one option in ArcGIS for storing text to
place on your maps.
Label is the main alternative to annotation. A label's
text and position are generated dynamically according
to a set of placement rules.
Building a Geodatabase
Design
geodatabase
• Building a geodatabase
– Designing the geodatabase
• (Think before your create)
Create a new
geodatabase
– Creating a new geodatabase
• (Name and location only)
– Defining the geodatabase
structure
Defining GDB
structure
• (Schema and data)
– Entering spatial data
• (Loading or automation)
Geodatabase
Entering spatial
data
– Define additional properties
• (Validataion, relationships, networks)
Define additional
properties
Designing a Geodatabase
• Conceptual Plan: Current and future needs
–
–
–
–
–
Data contents
Coordinate system
Data validation and modification rules
Relationships among objects
Custom objects
• Logical Design
– What needs to store (Not how to store)
Creating a New Geodatabase
• Create a new geodatabase using ArcCatalog
– Create new
– Rename default name
GISC 6382 Applied GIS UT-Dallas Briggs
44
• Exercise:
– Topology
– Join
• GIS Take-Home (Join/Relate) by email
• Kandilli Campus Tour (April 26 Friday at 2:30 pm)
– Private American High School (Robert College)
– Disaster Preparedness Education Unit (Eq. Simulation)
– National Eq. Mon. Center
– Museum (Historical Equipments)
– Astronomy
– Geodesy
• Seminar by ESRI Turkey Firm (İşlem) (April 29 Monday at 9.30 am)
at Demir Demirgil Hall/South Campus)