ATS2780 Lecture 7: Digital Representations of Geographical Space and GIS
25 May 2018
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Lecture 7 - Digital Representations of Geographical Space and GIS
The Object View of the World
• Object or Entities
o Represents the geographical space as objects with well-defined
boundaries in empty space
o Geographical space
▪ An empty container
▪ Different sorts of objects
o Objects
▪ Well defined boundaries
▪ Countable
▪ Identifiable by their dimensionality
• Areas (polygons), lines and points
▪ Can be a location
o Attribute: e.g. date
• Point objects:
o Historical buildings
o Post offices
o Telephone boxes
• Line objects:
o Railway line
o Tram routes
• Area objects:
o Victoria market
o Flagstaff gardens
o Carlton gardens
The Field View of the World
• Represents the geographical space using a number of variables, each
measurable at any location and changing in value continuously across space
o Geographical space
▪ Not an empty container, but continuous fields or surfaces
▪ Everywhere has a value or sets of values
o Continuous fields or surfaces
▪ Distinguished by what is being measured at each point
▪ Value is a function of location
• Types of continuous fields
o Numerical continuous fields
▪ Soil properties
• E.g. pH, soil moisture
▪ Atmospheric temperature, pressure, rainfall
o Categorical continuous fields
▪ Soil type
▪ Land use and land cover
▪ Such fields change suddenly at the boundaries between
different classes
Choosing the Representation
• Depend on what you want to do with the spatial representation
find more resources at oneclass.com
find more resources at oneclass.com
o A corporation concerned with the management of facilities may
consider an object view
o An environmental protection agency may take a field view to allow
analysis of hazards in the environment
o Most analyses and modelling in environmental science take the field
view
o Representing population density as continuous fields can be useful for
visualisation and analysis
• Digital representations
o More interested in spatial representation in digital form
o Two basic forms of digital spatial representations
▪ Vector - the object view
▪ Raster - the field view
Vector Representation
• Objects are represented as points, lines or areas
• All are represented using coordinates
o One per point
o Areas as polygons
o Lines as polylines
• Each object also has an associated attribute or several attribute values, which
are stored separately from coordinates
• A vector representation of a reservoir and highway
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find more resources at oneclass.com
Raster Representation
• Divide the geographical space into square cells
• Each cell has a value
• Represent discrete objects as collections of one or more cells
• Represent fields by assigning attribute values to cells
• More commonly used to represent fields than discrete objects
• Each colour represents a different value of nominal scale field denoting land
cover class
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Lecture 7 - digital representations of geographical space and gis. The object view of the world: object or entities, represents the geographical space as objects with well-defined boundaries in empty space, geographical space, an empty container, different sorts of objects, objects, well defined boundaries, countable. Identifiable by their dimensionality: areas (polygons), lines and points, can be a location, attribute: e. g. date, point objects, historical buildings, post offices, telephone boxes, line objects, railway line, tram routes, area objects, victoria market, flagstaff gardens, carlton gardens. Spatial data: two types of spatial data, vector data and raster data, all are produced by measuring the locations and characteristics of geographical entities, components of spatial data, location, attribute, time. A container of maps or georeferenced images in digital form (such as google earth and maps) A computerised tool for solving geographical problems (e. g. land use conflicts) A spatial decision support system (e. g. site selection, routing, land use optimisation)
