Representations Occur: In the human mind, when information is acquired through the senses and stored in memory In photographs, which are two-dimensional models of light received by the camera In written text, when information is expressed in words © 2005 John Wiley & Sons, Ltd

Digital Representation Uses only two symbols, 0 and 1, to represent information The basis of almost all modern human communication Many standards allow various types of information to be expressed in digital form MP3 for music JPEG for images ASCII for text GIS relies on standards for geographic data © 2005 John Wiley & Sons, Ltd

Why Digital? Economies of scale Simplicity Reliability One type of information technology for all types of information (all MM elements) Simplicity Reliability Systems can be designed to correct errors Easily copied and transmitted At close to the speed of light © 2005 John Wiley & Sons, Ltd

Accuracy of Representations Representations can rarely be perfect Details can be irrelevant, or too expensive and voluminous to record and comprehend It’s important to know what is missing in a representation Representations can leave us uncertain about the real world © 2005 John Wiley & Sons, Ltd

The Fundamental Representation Problem Geographic information links a place, and often a time, with some property of that place (and time) “The temperature at 34 N, 120 W at noon local time on 12/2/99 was 18 Celsius” The potential number of properties is vast In GIS we term them attributes (db) Attributes can be physical, social, economic, demographic, environmental, etc. Time can express: Data Quality Dynamic Data Trend © 2005 John Wiley & Sons, Ltd

CHAPTER 2: Geographic Data and the Database Data and information: Datum: a single number or fact , is a singular of Data( number, letter, or text) single entry in the database Data : a collection of facts in the database , multiple enrty in the database , and is plural of datum Data set : is a collection of related data, usually associated with a specific topic Information : the meaning or interpretation of data, is the knowledge obtained from data See maps from the book( p.g 30)

CHAPTER 2: Geographic Data and the Database GIS uses spatial data as its primary component , but the term geographic data is more appropriate What is Spatial Data? Spatial data occupies geographic space, it has specific locations according to some world geographic referencing system, such as latitude-longitude

Types of GIS Spatial Data Spatial data is classified as three main types’ features or landscape elements: Point: is a spot or location that has no physical or actual spatial dimensions, but does have specific location. Line: is a one dimensional feature having only length no width, it has a beginning and an end Polygon: is an enclosed area , a 2D feature with at least three sides and that has area and perimeter(محيط للشكل) (Pictures pg 34)

Types of GIS Spatial Data GIS themes are usually stored as point, line, or polygon features data file, so the type of feature must be declared so that the GIS can properly identify and manage the data, for example line feature should not be confused with one side of a polygon.

Discrete Objects and Continuous Fields There are two basic types of measures of the geographic landscape, both of which characterize the environment , but in different ways Discrete Data: there are distinct features that have definite boundariesوThe most fundamental distinction in geographic representation Discrete objects The world as a table-top Objects with well-defined boundaries © 2005 John Wiley & Sons, Ltd

Discrete Objects (Features) Points, lines, and areas Countable Persistent through time, perhaps mobile Biological organisms Animals, trees Human-made objects Vehicles, houses, fire hydrants © 2005 John Wiley & Sons, Ltd

Continuous Fields Continuous Data: does not have definite boarders or distinctive values, a transition from one measure to another is implied Properties that vary continuously over space Value is a function of location Property can be of any attribute type, including direction (Pictures pg 36) © 2005 John Wiley & Sons, Ltd

Phenomena conceptualized as fields Phenomena conceptualized as fields. The illustration shows elevation data from the Shuttle Radar Topography Mission draped with an image from the Landsat satellite, looking SE along the San Andreas Fault in Southern California, plus a simulated sky

Difficult Cases Lakes and other natural phenomena Weather forecasting Often conceived as objects, but difficult to define or count precisely Weather forecasting Forecasts originate in models of fields, but are presented in terms of discrete objects Highs, lows, fronts © 2005 John Wiley & Sons, Ltd

GIS Data Characteristics There are numerous properties that make geographic data more functional and valuable, so it is important to understand these major characteristics in order to take full advantage of GIS. Location (position): is a major starting point of spatial measurement, location can be descriptive ( as in the old days), today better means of location are required (map A) © 2005 John Wiley & Sons, Ltd

GIS Data Characteristics, Cont Size :polygon has area and line has length Shape: often indicates identity and on the landscape, and are quickly appreciated by the eye, but the computer need special programs to make spatial from descriptions.(mathematical techniques) Figure pg 38 © 2005 John Wiley & Sons, Ltd

Spatial Data relationships GIS is an excellent tool for determining such characteristics, and the human must decide the meaning of those relationships, but the GIS offers insight , in the following some spatial relationship Distance: distance from one feature to another is an important relationship (see picture), determining the distance between cities easy but in emergency? © 2005 John Wiley & Sons, Ltd

Spatial Data relationships Distribution :is the collective locations of features , Density: is the number of items per unit area: how close feature to each other Pattern: is the consistent arrangement of features , similar to distribution and density Figure pg 41 © 2005 John Wiley & Sons, Ltd

Proximity Relationships Connectivity: consider features that connect, or at least touch Contiguity (التماس) :one aspect of connectivity , is the degree of connectivity , Illustrated four degree of connectivity :none, weak, strong, and enclosed © 2005 John Wiley & Sons, Ltd

Proximity Relationships Connectivity: consider features that connect, or at least touch Contiguity (التماس) :one aspect of connectivity , is the degree of connectivity , Illustrated four degree of connectivity :none, weak, strong, and enclosed © 2005 John Wiley & Sons, Ltd

Proximity Relationships,cont Adjacency (الجوار) : is the nearness features , the meaning of adjacency must be interpreted by the user for any given situation . for example determining the number of village within 10 kilometers of point x. © 2005 John Wiley & Sons, Ltd

Time and GIS data Time is an important data quality element it can be used or expressed in terms of data quality , dynamic data (changing data), and trends these are temporal components of geographic data that can be very important in understanding a population project needs up-to-date and consistent data

Time and GIS data,cont geographic data is dynamic and often time is an important attribute features can change shape, size, position , and attribute over time for example (natural of seasonal changes, population growth, vegetation growth, and city evaluation this is particularly true of natural hazard events , such as floods, and volcanic eruptions

Trends Temporal trends: are determining from comparisons of data over time Spatial Trends: are determining from comparisons of data over space Geographic trend can be purely spatial (changing size, shape, or position of features over space and/or time Nonspatial evolving attributes ,such as growing population or changing value of some type

GIS project, Data files, and Themes A GIS project contains at least several themes GIS theme include one or more data sets dealing with particular topic Each theme in a project is defined as a point, line, or polygon, and each is stored in separate data files to avoid confusion of different data types

The GIS Database Without Database , GIS would be little more then computer cartography(فن رسم الخرائط) GIS Data comes from many sources The central data integrator for GIS is the database GIS accepts and merges diverse databases and different types of data. . © 2005 John Wiley & Sons, Ltd

Cont Database in GIS is a simple concept, a list or table of data arranged as rows and columns One of the best types for GIS is relational database, it is possible for ask questions ,and looking for conditions in each , which called conditional query © 2005 John Wiley & Sons, Ltd

Database –Map Link A major strength of GIS is the interactive link between the database and the map When selection are made in the database, the selected records are highlighted on the map. When features are selected on the map, they are highlighted in the database. © 2005 John Wiley & Sons, Ltd

The Database Approach The GIS database approach is a simple concept with two basic aspects The first one is that the database is central to GIS projects which offer several benefits( convenience, reduced redundancy and errors, sharing, flexibility, and standardization) © 2005 John Wiley & Sons, Ltd

The Database Approach The GIS database approach is a simple concept with two basic aspects The first one is that the database is central to GIS projects which offer several benefits( convenience, reduced redundancy and errors, sharing, flexibility, and standardization) © 2005 John Wiley & Sons, Ltd

Cont The second important aspect which is that much of the data processing and analytical operations take place in the database when possible This approach dose not diminish the role of map graphics. © 2005 John Wiley & Sons, Ltd

Thank you