Migration Measures and Geospatial Visualisation Flashcards
What is a Migration Matrix?
− Origins in columns, destinations in rows.
− The totals at the ends represents the total out/in migration for each place
What is GIS?
− Communicates geospatial (geographic) information in ways that, when combined with human understanding, allows for data exploration and decision making processes
− Use of computer technology for exploring data in visual form
− Use of computer graphics for acquiring a deeper understanding of data
− A need to adopt the most suitable form of visualisation for the data/purpose
What are significant developments in GIS in the past 30 years?
− The computing technology for storing and processing spatial data
− The software available for analysis and visualisation
− Games industry has pioneered creation of ‘virtual reality’
− Geographers have begun using new visualisation technologies E.g. 3D maps (building heights)
What are some Visualisation problems and their solutions?
− too many polygons − size of polygons too small Solutions − Zoom in & map only certain areas − Use another form of mapping e.g. cartograms
What are Cartograms?
− Cartograms used when distortions in size, and occasionally shape or distance, are made explicit and are seen as desirable – we might want distortion!
− Typically places on cartograms are drawn so that their size is in proportion to some attribute e.g. their population as opposed to conventional land area
What is an Isodemographic Map?
− A diagrammatic method of displaying countries, administrative areas or zones within a country in two-dimensional maps with each area directly proportional to the population density of the country or jurisdiction
− To provide a framework for the analysis and communication of social and economic variables (Dorling)
What are circular Cartograms?
− Each region is drawn as a circle with its area proportional to its population
− “Each region … is treated as an object in a gravity model which is repelled by other overlapping circles but is attracted to circles which were neighbouring regions on the original map” (Dorling, 1995, p. 32)
− Circles are moved about by repulsion and attraction forces
− Cartogram of non-overlapping circles produced after a few hundred iterations
What are the uses of Cartograms?
− To show variations over space (as with conventional base maps)
− Alternative base maps for use in research
− To show distributions that are concealed by conventional mapping – some areas are too small if they have a high population density
− Ability to shock and provide impact
− Easy bi-variate mapping
− More socially just form of mapping because they give people more equitable representation – variable being mapped has greater importance than land area
What are some problems with Cartograms?
− People who understand less about geospatial knowledge may not be able to interpret properly.
− Not entirely geographically accurate, so needs consideration.
Name the methods of creating Cartograms
− Physical accretion models − Mechanical methods − Competing cartogram algorithms − Circular cartograms − Cellular automata cartograms − ScapeToad − Cartogrammer
What is Flow Mapping?
− Use of lines of differing width to depict movement of goods or people
− Waldo Tobler was amongst the early pioneers of producing automated migration flow maps
– Ravenstein (1885) mapped currents of migration just as flows crossing borders
