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GIT 214 > 6 - Topology > Flashcards

6 - Topology Flashcards

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1
Q

Spatial data model

A

Simplified representation of spatial
features or spatial phenomena on the Earth’s surface

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2
Q

How is vector data prepared??

A
  1. Geometrical data are stored as sets of xy coordinates.
  2. The data & their spatial relationships are organised into digital data files that the computer can access, interpret and process.
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3
Q

Components of general format for storage of vector data

A
  1. The object Id-number, which has to be unique
  2. The n-term
  3. The co-ordinate pairs as defined by n-term
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4
Q

The object Id-number use

A
  • Has to be unique
  • Used to identify the object and to link attributes to it
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5
Q

The n-term use

A

States how many pairs of co-ordinates are used to build the object

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6
Q

Difference bwtn spaghetti and topology models

A

The level of structure and organisation of the data

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7
Q

Topology def

A
  • The spatial relationships that exists between features in a feature layer in the vector model.
  • Set of rules of how points, lines and polygons share their geometry.
  • The geometric relationship between edges (line), nodes (point) and the faces (polygon), they created.
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8
Q

What does topology do?

A

Checks and validates the spatial relationship of neighbouring and overlapping features.

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9
Q

Nodes def

A

Connections at the intersection points and start at end points of edges

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10
Q

Edge def

A

Set of coordinate pairs starting with a node and ending with a node making up the boundaries of
polygons.

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11
Q

Face def

A

The largest two-dimensional space restricted by the edges

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12
Q

Some topology rules

A
  • Municipal boundaries must not overlap.
  • Municipal boundaries must not have gaps (slivers).
  • Polygons showing property boundaries must be closed.
  • Undershoots (lower than final value) or overshoots (higher than the final value) of the border lines are not allowed.
  • Contour lines in a vector line layer must not intersect.
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13
Q

Main topology rules

A
  1. Connectivity
  2. Adjacency
  3. Containment
  4. Contiguity
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14
Q

Connectivity

A

Describes the linking of points or polygons to each other.

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15
Q
  1. Adjacency
A

Summarizes the sharing of a common boundary of two
regions or polygons.

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16
Q
  1. Containment
A

Features within a another specified feature

17
Q

Contiguity

A

Arcs (lines) have direction

18
Q

Arc-node topology

A
  • a from-node (starting node) indicating where the arc begins
  • a to-node ( ending node) indicating where the arc ends.
  • Between each node pair is a line/arc segment = link
19
Q

Polygon-arc (area)

A
  • Arc that connects to surround an area defines a polygon.
  • arcs are used to construct polygons, and each arc is stored only once.
20
Q

Polygons that share an arc are deemed…?

A

Adjacent or continuous

21
Q

Advantages of topology

A
  1. Ensures data quality/ Enables error detection
  2. Enhance spatial analysis
  3. Represent the spatial information as well as spatial relations
  4. Shows how objects correspond to one another
21
Q

Disadvantages of topology

A
  1. Complex
  2. Time consuming to build depending on the number of features
    and relationships to specify
  3. Data integrity concerns
22
Q

Ensures data quality - Enables error of detection of:

A

nsures data quality - Enables error detection of:
❖ Undershoot - lines that don’t meet
❖ Overshoot
❖ Polygons that don’t close
❖ Polygons that overlap

23
Q

Enhances spatial anaylyse

A

Include spatial and attribute data (increase in volume/storage)

24
Q

Examples of analyzing vector data

A

❖ Network analysis (e.g. finding the best route across a road network) or
❖ Measurement (e.g. finding out the length of a river)

25
Q

Topological error examples

A
  • Point features may not be at the intersection point of line features
  • Polygon features are not closed properly
  • Contact points do not coincide
  • Overlaps or gaps in polygon features . Since neighbouring or same location features are represented twice, there is no full coincidence at the point and line features.
  • Neighbourhood relations are unclear
  • Due to exclusion of information, polygon, point or line features included in polygons are unclear.
  • Navigation is not possible since there is no direction concept in the line features.
26
Q

Why use shapefiles if it does not include topology?

A
  • Displays more rapidly
  • Format is non-proprietary and interoperable - can be used
    across different software packages.
27
Q

Industry standard for vector data files

A

SHAPEFILES

28
Q

Non-proprietary def

A

freedom from exclusive ownership / not registered or protected as a trademark or brand name; generic.

29
Q

Interoperable

A

able to exchange and make use of information

GIT 214 (16 decks)

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