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

Topics for Today 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 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 Data The “geographic matrix” (Berry 1964): –Places (or locations) –Characteristics (or attributes) –Time

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 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.

Representing Geographic Space Model examples –Map –Blueprint –Organizational chart

Representing Geographic Space A Map is not a treasure It communicates its location

Representing Geographic Space A Blueprint is not a house It communicates its design

Representing Geographic Space An organizational chart is not the staff It represents their relationships

Representing Geographic Space Model use advantages –Easier to understand at a glance –No need to trace through narrative descriptions of relationships –Communicates one clear definition

Representing Geographic Space 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.

Representing Geographic Space 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).

Representing Geographic Space 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)

Representing Geographic Space Object based sample points Field based fill areas

Representation 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?

Representation of Relationships 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.

Representation of Relationships 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 Geographic Data The Basics –Bit –Byte –Integer –Floating point –Double precision

Source: Chrisman 1997

Data 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 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 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 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 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 Models Logical Data Models: –Hierarchical Data Model –Network Data Model –Relational Data Model –Object-Oriented Data Model –Object-Relational Data Model

Source: Burrough 1986

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

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.) 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.) 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: 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.

Geodatabases 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: Spatial Data Models: –Vector data model (Vector representation) Lo, Chapter 6 –Raster data model (Raster representation) Lo Chapter 5

Example Quiz Questions 1.Define GIS 2.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 Questions 11. 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 27 th Read 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