Transcript Introduction to GIS for the Purpose of Practising PGIS

Support the spread of “good practice” in generating, managing,
analysing and communicating spatial information
Introduction to GIS for the
Purpose of Practising PGIS
Visualising Spatial Information
and Relationships
By: Jon Corbett and Kasondra White
Unit: M12U02
Visualising spatial information
and relationships
• Communicating spatial phenomena and
ideas
• Enhancing dialogue
• Displaying data
• Confidence in data
• Map types
• Symbols
Displaying data
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Different types of data are used by GIS
File format represents data type
Distinguished by file extension
Some examples include:
– .shp
– .dbf
– .prj
Raster data
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Pixels are used to represent images
Image divided into a grid
Each cell contains information
Straightforward and easily understandable
visualisation
• Quality lost when image is magnified
• Require more storage space
Raster data
Raster data
Vector data
• Based on points, lines and polygons
• Mathematical representations of images
• Accuracy of geographic features
maintained
• Less capable of representing continuous
images
Vector data
Revisiting the layer
• Geospatial data are organised into
different themes
• Arranging layers hierarchically
• Examining interrelationships between
layers
• Overlay – using one or more thematic
layers to create a new map or series of
maps
Confidence in data
• Understanding data origins
• Examining metadata (i.e. data about other
data)
• It is important to:
– be aware of the range of data covered
– know when the data were collected
– understand the goals of the individual or
agency responsible for creating the data
Database management
• Attribute tables
• Adding information
to pre-existing layers
• Viewing data on the
map
• Viewing data within
the Attribute Table
Types of data
• Attributes
– characteristics associated with features on the
map
– information is displayed in Attribute Tables
• Examples of attribute data include:
– the square footage of a building
– the names of land-use types
– average incomes of inhabitants
– names of community locations or routes
Types of data
• Spatial data
– define the absolute position of an object
– use X and Y coordinates
– reflect size and shape in real world terms
– features must be aligned with known
geographic locations (“georeferencing”)
Map types
• Maps are:
– stylised representations of the world
– abstractions
– a representation of the Earth’s surface
• Features included are at the map maker’s
discretion
• Constant rate of change means maps are
often out of date
Aerial photos
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Digital images of the Earth from the air
Raster images
Can be a useful base layer
Fairly accurate representations
Subject to pixelisation when magnified
Aerial photos
Line maps
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Generally vector images
Illustrate features using lines and symbols
Street maps
Used for drawing out specific points of
interest
Line maps
Topographic maps
• Concerned with depicting the topography
of the Earth’s surface
• Characteristics of features such as:
– lakes
– mountains
– human-made items
• Depict contours and elevation of features
Topographic maps
3-D
• Aligns more closely with how human
beings see information
• Adds an element of depth
• Uses a Z coordinate
3-D
Symbols
• GIS employ a range of
symbols to represent
features
• Used to reference
specific points on a
map
• Align with X and Y
coordinates
• Convey meaning
independent of
language