Geographic Information Systems (GIS) in Environmental Studies · 2. It provides efficient encoding...
Transcript of Geographic Information Systems (GIS) in Environmental Studies · 2. It provides efficient encoding...
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Geographic Information Systems (GIS)in Environmental StudiesENVS 6189 3.0 – Winter 2003Session III
John Sorrell
York [email protected]
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Session PurposeSession Purpose::
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To discuss the various concepts of space, the dominant data types, themes and models used to represent and organize geographic information.
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Cognitive RepresentationCognitive Representationof Spaceof Space::
GIS in Environmental Studies
Humans have many conceptualization of space. A few include:
• Figural Space• Vista Space• Environmental Space• Geographic Space
Existing GIS is concerned largely with Geographic Space
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The Nature of The Nature of Geographic DataGeographic Data::
For effective use in a computer environment, geographic data entities have the following characteristics:
GIS in Environmental Studies
1) Geographic Position:a location specified in a unique way (where is it).
2) Attributes:non-spatial descriptions of the feature (what is it).
3) Spatial Relationships:selected relationships among features explicitly defined (what’s around it)
4) Time:referring to a point or period in time as defined in real
world or database time-units (when is it).
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Descriptions of Geographic Descriptions of Geographic Data Organization:Data Organization:
Spatial Organization:• Disaggregated Data – Individuals or Single Entities;• Aggregated Data – Mass observations defined by criterion.
Temporal Organization:• Cross-Sectional –data in a single time period;• Longitudinal – one discrete are over a series of observation periods.
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Spatiotemporal Relationship:• Geometric Transformation – spatial change of
location, and/or properties of object (TSA).• Very complex in a database when recorded changes
effect location, attributes and relation to other objects .
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Geographic Data Geographic Data Themes:Themes:
Social-Economic Data:
Information about humans, their activitiesand the spaces/structures used;
Examples: • Land Registry Data, Municipal By-law maps, Demographics, Retail Activity, Transportation Networks.
Sources: Government – Private Database - Field Surveys;
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Considerations/Constraints: Cost, Quality, Format, Time.
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Data Themes Data Themes (cont’d):(cont’d):
Natural/Environmental Data:
Information about the natural or built environment.
Sources: Government – Private Database - Field & Lab Work;
Considerations/Constraints: Cost, Quality, Format, Time.
Characteristics:
- comparatively more static than human data;- mapping unit and scale may smaller scaled;- most effective when merged with human data.
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Modeling the Real Modeling the Real World:World:
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Data Model: A logical construct for organizing data in an information system.
Real World
User view level
Exact Object
Database level
Graphic Mode level
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Spatial Data Spatial Data Models:Models:
Data Structure: A logical and physical mean for digitally encoding geo-spatial data.
A. study area
B. raster representation C. vector representation
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Characteristics of Characteristics of the Raster Data the Raster Data Model:Model:
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Cell value
Spatialresolution
Coordinate Referenceof end of point
Coordinate Referenceof start of point
Different attributesstored in different layers
Pixel
Spatial unit
Column no.Row no.
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Raster Data Model:Raster Data Model:Representation of Data
in Raster FormatData Layerin Map Form Overlay Analysis
Forest Types
Soil Types
Topography
Forest Types
Soil Types
Topography
Analysis ResultsStudy Area
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Vector Data Model:Vector Data Model:(Arc(Arc--Node Topological Node Topological data model)data model)
Topology: a branch of math that defines spatial relationships between features and their properties in elastic space.
Triangulated Irregular Network (TIN)
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The Vector Data Model The Vector Data Model –– Spatial Spatial Representations:Representations:
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Vector Layers
Vector map
Actual terrain
forest
drainage area
drainage lines
drainage point
highway layer
•
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Geographic Data Geographic Data Types:Types:
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Vector (Point, Line Vector (Point, Line Polygon)Polygon)
Raster Raster (Images)(Images)
3D3D
CADCAD
Raster Raster (Surface)(Surface)
TabularTabular
GI Data uses wide variety of data types GI Data uses wide variety of data types and Forms:and Forms:
Geo-referenced data (features):Geo-referenced data forms the locations and shapes of map features such as buildings, streets, or cities. This data intrinsically includes location as a key variable (x,y) .
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“Combined Spatial Layers”
interrelated datapowerful analysis toolseasily understood and presentable co-relationslink data through common geography
Zoning
Topography
AdministrativeBoundaries
Statistical Data
Central Offices
Road Networkand Addresses
ClientsCombined Data ModelsCombined Data Modelsand Thematic Layers:and Thematic Layers:
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ComparisonComparisonof Raster & of Raster & Vector Model:Vector Model:
Advantages:1. It provides a more compact data
structure than the raster model.2. It provides efficient encoding of
topology, and, as a result, more efficient implementation of operations that require topological information, such as network.
3. The vector model is better suited to supporting graphics that closely approximate hand-drawn maps.
Advantages:1. It is a simple data structure.2. Overlay operations are easily and
efficiently implemented;3. High spatial variability is
efficiently more efficient represented in a raster format
4. The raster format is more or less required for efficient manipulation and enhancement of digital images.
Disadvantages:
1. The raster data structure is less compact.
2. Topological relationships are more difficult to implement.
3. The output of graphics is less aesthetically pleasing because boundaries tend to have a block appearance.
RASTER MODEL
Disadvantages:
1. It is a more complex data structure than a simple raster format.
2. Overlay operations are more difficult to implement.
3. The representation of high spatial variability is inefficient.
4. Manipulation and enhancement of digital images cannot be effectively done in a vector domain.
VECTOR MODEL
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