GIS for Environmental Science ENSC 3603 Class 4 1/22/09

GIS for Environmental GIS for Environmental ScienceScience

ENSC 3603ENSC 3603

Class 4Class 41/22/091/22/09

Topics for Topics for TodayToday

• Representation of Geographic Data• Places, Characteristics, Time

• Concepts of Spatial Data• Entity, Attribute, Relationship

• Representing Geographic Space• What is a Model

• Object-Based model

• Field-Based Model

• Representation of Relationships• Spatial

• Temporal

• Digital Representation of Geographic Data

Topics continuedTopics continued• Data Organization in the Computer• Data item, Record, File, Database, Metadata

• Data Classification

• Feature codes and Feature coding

• Data Models• Conceptual, Logical, Physical

• Relational, Object-oriented, Object-relational, Geodatabase

• Computer Representations of Geographic Data• Vector Data Model

• Raster Data Model

Representation of Geographic DataRepresentation of Geographic Data

• The “geographic matrix” (Berry 1964):

– Places (or locations)– Characteristics (or

attributes)– Time

Vaughn Skinner

datamodel.ppt

• Concepts of spatial data:• Entity – An entity is a spatial object with specific properties• Attribute – a property of an entity• Relationship – how entities relate

• Entities with common properties are called: entity class, entity type and feature class

Representing Geographic SpaceRepresenting Geographic Space

• What is a Model?• A tentative description of a system or theory that

accounts for all of its known properties.”…American Heritage Dictionary

• A model is an abstract representation of some real thing. • The representation (or type of model) will vary

depending on what kind of thing is to be modeled.• Fundamental modeling activities are the same

regardless of model type.


• Model examples– Map– Blueprint– Organizational chart


• A Map

is not a treasureIt communicates its location


• A Blueprint

is not a houseIt communicates itsdesign


• An organizational chart

is not the staffIt represents theirrelationships


• Model use advantages– Easier to understand at a glance– No need to trace through narrative

descriptions of relationships– Communicates one clear definition


• Model activities• Identify – Determine what is to be represented in the

model.• Name – Each thing represented in the model needs to

have a unique and meaningful name.• Describe – Name is important, but not sufficient.

Description should be no more than three sentences, each with subject, object, and verb. Must answer:– What is it?– What it is not.– Sometimes: List examples.

• Associate – Much of the meaning is in associations among the things represented in the model.


• Object-based model:– It treats geographic space as populated by discrete

and identifiable objects.– Two classes of spatial objects:

• Exact objects with well-defined boundaries• Inexact objects with fuzzy boundaries

– Spatial objects are often represented as points, lines, and polygons (i.e., vector data model).


• Field-based model:– It treats geographic space as populated by one or

more spatial phenomena, which are real-world features that vary continuously over space with no specific extent.

– Spatial phenomena are represented as surfaces in the forms of either regular tessellations (e.g., raster grid) or irregular tessellations (e.g., Triangulated Irregular Network – TIN).

– (Lo, 2007 p. 69)


Object basedsample points

Field based fill areas

Representation of RelationshipsRepresentation of Relationships

• Spatial relationships:– Also known as “topological relationships” in GIS,

which are critical to spatial analysis in GIS.– Adjacency - Washington County is adjacent to Benton

County.– Connectivity - Garland Ave is connected to Maple St.– Containment - U of A is inside City of Fayetteville.– What about “Prairie Grove is near Fayetteville”?

What is near?


• Temporal relationships:– Almost all commercial GIS today represent snapshot

data; i.e., data at one point in time.– Most changes take place in the real world are caused

by various processes (e.g., urban sprawl, air pollution) that involve spatial changes over time (i.e., relationships between space and time).

– However, spatiotemporal GIS is still pretty much a research topic.


• Temporal attributes of Geographic Processes– Generation time – Time of object creation.– Duration time – Time of object existence or

observation.– Temporal significance – The importance of an object

or event.– Temporal scale – The ratio between map time and

actual time. Use 12 s to display images over a 24 hour period.

Digital Representation of Digital Representation of Geographic DataGeographic Data

• The Basics– Bit– Byte– Integer– Floating point– Double precision

Source: Chrisman 1997

Data Organization in the ComputerData Organization in the Computer• Data item (also known as data fielded, attribute item):

– An occurrence or instance of a particular characteristic pertaining to an entity. (An entity is a spatial object with specific properties.)

• Record:– A record contains related data items of the same entity.– It’s often represented as a row in a table.– In database, it’s also called a stored record or tuple.

Data Organization in the ComputerData Organization in the Computer• File:

– Formed by grouping related records together.

• Database:– A collection of persistent data stored in a database

management system (DBMS) so it can be shared and used by different users in an organization.

• Metadata:– Data about data.

(Lo, 2007 p. 79).

Data ClassificationData Classification

• A Classification schemes:– Descriptive names of classes and subclasses

• Based on form or function

– Definitions of the classes and subclasses• In a land use scheme a two story building is

recorded as “building” according to its form and “Laboratory” according to its function.

• USGS Land-use/Land-cover Classification has 4. Forest land as a Main class and 41. Deciduous forest and 42. Coniferous forest as a Subclass.

Feature codes and Feature CodingFeature codes and Feature Coding• Entities and attributes are represented in the form of

feature codes that consist of major codes and minor codes.– USGS Land-use/Land-cover Classification has major

code 4. Forest land and minor codes 41. Deciduous forest and 42. Coniferous forest.

Data ModelsData Models• Data model - a description of our view of the real

world.• Three levels of data models:

– Conceptual data model:• represents the user’s perception of the real world (i.e., How

do you conceptualize the real world to solve your specific problem?)

• e.g., entity-relationship (E-R) data model

– Logical data model:• represents an implementation-oriented view• Three classical logical data models are: relational data

model, network data model, and hierarchical data model.• Two more recent logical data models are: object-oriented

data model and object-relational data model

– Physical data model:• Describes the physical storage of the data in the computer.

Data ModelsData Models

• Logical Data Models:

– Hierarchical Data Model

– Network Data Model

– Relational Data Model

– Object-Oriented Data Model

– Object-Relational Data Model

Source: Burrough 1986

Source: Burrough 1986

Relational Database ModelRelational Database Model

• Relational data model is probably the most used computer database model.

• A table is a relation• A row in the table is called a tuple• The column name is called a field or attribute• The type of values in each column is a domain.

Tuple

Data field

Relation

Relational Data Model

Source: Aronoff 1993



Structured Query Language (SQL):

SELECT <attribute_name> FROM <table> WHERE <condition_statement>

e.g., SELECT * FROM “Attribute Table 1” WHERE “Stand Number = J-127”

Object-Oriented (OO) Data Model:Object-Oriented (OO) Data Model:

• Data are defined in terms of objects, which in turn are organized into groups of similar phenomena (known as object classes).

• The characteristics of an object may be described in the database in terms of its attributes (known as state) as well as a set of procedures that describe its behavior (known as methods).

Object-Oriented Data Model : (cont.)Object-Oriented Data Model : (cont.)

• Once the data is encapsulated within an object, the only way to change or query the data is to send a request (known as a message) to carry out the requested operation.

• Same message may generate a different reaction when received by different objects or in a different context (known as polymorphism).

Object-Oriented Data Model : (cont.)Object-Oriented Data Model : (cont.)

• Hierarchies can be established among objects to form super and sub classes. The defined states and methods of objects are passed down through the hierarchical structure (known as inheritance).

• OO database provides a very efficient structure for queries with reference to specific objects, while RDBMS is better for queries based on attribute values.

Object-Relational Data Model:Object-Relational Data Model:

• Supports geographic objects (with properties, behavior, and relationships) in a relational database management environment. In other words, it is a mixture of relational approach and object-oriented approach.

• The Geodatabase data model of ArcGIS 9.3 is an example of object-relational data model. Oracle Spatial is another example.

GeodatabasesGeodatabases

A geodatabase stores a feature class as a table in an RDBMS. Each feature is a row in the table. The vector shape of the feature is stored in the table's Shape field

“The geodatabase is a vector data format that stores point, line, and polygon data in a relational database management system (RDBMS) table. The defining purpose of this data format is to allow you to make the features in your GIS datasets "smarter," by endowing them with natural behaviors and to allow any sort of relationship to be defined among features. With geodatabases, you also have the option of creating your own custom features, such as complex electrical junctions that have their own behavior. “ (ESRI)

Spatial indexing is created to expedite the search of spatial objects in a database

Computer Representations of Geographic Data:Computer Representations of Geographic Data:

• Spatial Data Models:

– Vector data model (Vector representation) Lo, Chapter 6

– Raster data model (Raster representation) Lo Chapter 5

Example Quiz QuestionsExample Quiz Questions1. Define GIS2. How Does a GIS Store Information?3. What are the four components of a GIS as an

information System? 4. Name three types of geographic data.5. Name three types of people that use GIS.6. T or F. Early GIS systems were developed by

small companies and hobbyist.7. Name three Contributing Disciplines to GIS.• T or F. Natural resources management and

wetlands restoration are GIS Applications.

Example Quiz QuestionsExample Quiz Questions11. Entity, Attribute and Relationship are concepts of

_______________ data.12.T or F. A small scale map is best to represent the North

American Continent.13. What is the purpose of a map projection?14. Name the four map projection properties.15. A reference for the horizontal features on the earths

surface is a ______ _______.16. Arkansas is in State Plane Zone ______________.17. What are the primary operations that a GIS can perform

that make it a useful tool for solving problems?

For Next Tuesday the 27For Next Tuesday the 27thth

Read or doRead or do

Read Chapter 3 section 3.4 and 3.5 and chapter 6

• Study - for Quiz

Esri ArcGIS Desktop Module 1 due today

“The longer I live, the more I realize the impact of attitude on life… I am convinced that life is 10% what happens to me and 90% how I react to it. And so it is with you… we are in charge of our attitudes.” Charles Swindoll

• “The only disability in life is a bad attitude.” Scott Hamilton

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GIS for Environmental Science ENSC 3603 Class 4 1/22/09