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Questions and Answers
What is a key advantage of storing topological relationships in a Topologic Data Structure?
How does topology facilitate analytical functions in a Topologic Data Structure?
What type of data model represents geographic data as images in a regular grid of cells?
Why are Raster Data Models easy to read and write?
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What does each pixel in a raster data model typically represent?
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In the context of data models, what does the term 'cell resolution' refer to?
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What is a key characteristic of a Spaghetti Vector Data Model?
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What is an advantage of the Spaghetti Vector Data Model over the Topologic Vector Data Model?
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Why is overlay operation inefficient in the Topologic Vector Data Model?
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Which statement is a disadvantage of the Spaghetti Vector Data Model?
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What makes the Topologic Data Structure a more efficient choice for network analysis?
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What type of relationships are explicitly recorded in the Topologic Vector Data Model?
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Which model offers simpler data structure but with limited resolution compared to its counterpart?
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What is a disadvantage of the Spaghetti Vector Data Model?
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How are points, lines, and polygons stored in the Spaghetti Vector Data Model?
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Which type of model is efficient for display and plotting?
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What type of topological relationships are explicitly recorded in the Topologic Vector Data Model?
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Why is the Spaghetti Vector Data Model inefficient for most types of spatial analysis?
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Study Notes
Vector Topologic Data Model
- Advantages of topologic data structure:
- Efficient data storage for large data sets
- Enables analytical functions, such as:
- Modeling flow through networks
- Combining adjacent polygons with similar characteristics
- Identifying adjacent features
- Overlaying geographic features
Raster Data Models
- Raster formatting represents geographic data as images in a regular grid of cells
- Each cell (pixel) can be assigned attribute values
- Examples of raster data:
- Remote sensing images
- Scanned maps
- Grids (ArcGIS & ArcInfo specific)
- Graphical images (TIFF, JPEG, BMP, GIF, etc.)
- SRTM DEM (Digital Elevation Model)
- Raster grid properties:
- Each cell holds one value, even if it's empty
- Cells can hold an index standing for an attribute
- Cell resolution is given as its size on the ground
- Point and lines move to the center of the cell
- Minimum line width is one cell
- Rasters are easy to read and write, and easy to draw on the screen
Spaghetti Vector Data Model
- Each point, line, or polygon is stored as a record in a file with:
- ID
- List of coordinates defining geometry
- Examples of Spaghetti Vector Data Model:
- For points: ID, coordinates (e.g., 2, 1, 1, 3,4)
- For lines: ID, coordinates (e.g., 1, 2, 1, (0,1), (3,4), (5,6))
- For polygons: ID, coordinates (e.g., 1, 2, 1, (2,4), (4,3), (3,6), (2,4))
- Advantages:
- Simple and efficient for display and plotting
- Disadvantages:
- Inefficient for most types of spatial analysis
Topologic Vector Data Model
- Composed of points, lines, and polygons
- In addition to coordinate locations, topological relationships among geometric features are explicitly recorded
- Different topological relations exist for node, arc, and polygons
Comparison of Raster & Vector Data Model
- Raster data model:
- Pros: affordable, simple data structure, efficient overlay operation
- Cons: topology relationship difficult to implement, requires large storage, not suitable for all world phenomena
- Vector data model:
- Pros: efficient data storage, topological encoding more efficient, suitable for most usage, good graphic presentation
- Cons: overlay operation not efficient, complex data structure
Georeferencing of GIS Data
- Representation of the location of real-world features within the spatial framework of a particular coordinate system
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Description
Test your knowledge on the advantages of using topological data structure, such as efficient storage and quick processing of large data sets. Explore how topology facilitates analytical functions like modeling flow in networks and combining adjacent polygons with similar characteristics.
