This document discusses vector data in GIS. It begins by defining vector data as representing real-world features using points, lines, and polygons. It then describes the three vector types - points as single X,Y coordinates with no area or length, lines/polylines as a series of points with length but no area, and polygons as enclosed areas formed by connecting three or more points. The document provides examples of each vector type and how they can represent different landscape features. It also discusses attributes associated with vector data, common problems like slivers and overshoots/undershoots, and how vector data can be queried and symbolized based on attributes.

1. Vector data
Dr. Hans van der Kwast
OpenCourseWare
ocw.unesco-ihe.org

2. Learning objectives
After this lecture you will be able to:
• understand vector data models as used in GIS
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3. GIS Basics
2 common data models
to represent reality in a
GIS:
• Vector
• Raster

4. Vector data
• Vector data represents real
world features in a GIS
environment
• A feature can be anything that
you see in the landscape
• Features have attributes: text
or numerical information that
describe the features
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5. Vector types
Three types:
• Points
• Lines or polylines
• Polygons
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6. Points
• 1 X,Y location
• No area
• No length
• Display:
marker symbol, size, colour
• Applies to features:
•Without area
•Too small to be displayed at
current scale

7. Points
• Geometry consists of
only 1 vertex (node)
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8. Lines or polylines
• Series of X,Y points
• No area
• Have length
• Connectivity
• Direction
• Display:
Line stile, thickness, colour, offset
• Applies to features:
•Without area but with length
•Too thin to represent as an area at
the current scale

9. Lines or polylines
• Geometry consists of
2 or more vertices
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10. Polygons
• Enclosed region
• Area
• Display:
Fill pattern, fill colour,
outline pattern and colour
• Applies to features:
•Countries
•Provinces
•Catchments

11. Polygons
• Geometry consists of 3 or more
vertices and the last vertex is the
same as the first
QGIS training Uganda 11

12. Vector overlay
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• Points
• Polylines
• Polygons

13. Exercise vector
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• This map doesn’t have
a legend. In order to do
proper styling we need
to know which features
are
• Points
• Polylines
• Polygones
Source: OpenStreetMap.org

14. What can we do with vector data?
• Spatial queries, e.g.:
• Which houses are within the 100 year flood level of a river?
• Where is the best place to put a hospital so that it is easily
accessible to as many people as possible?
• Which learners live in a particular suburb?
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15. Common problems with vector data
• Accuracy of vectors depend on scale of digitizing
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Digitized from 1/1000000 map Digitized from 1/50000 map

16. Common problems with vector data
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Slivers

17. Common problems with vector data
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Overshoots and undershoots

18. Vector attributes
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Attribute data are used to describe features

19. Vector attributes
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20. Vector attributes
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21. Attributes for vector symbology
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Coloured by roof colour Coloured by presence of balcony

22. Search by attributes
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23. Attributes in detail
Attribute
Table
Field 1 :
YearBuilt
Field 2:
RoofColour
Field 3:
Balcony
Record 1 1998 Red Yes
Record 2 2000 Black No
Record 3 2001 Silver Yes
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Fields represent properties of the feature.
Can you think of other attributes that we can connect to houses?

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25. Acknowledgements
• Examples were taken from:
A Gentle Introduction to GIS
http://docs.qgis.org/2.6/en/docs/gentle_gis_intro
duction/
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