1106: Geographical Information: a primer

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1106 Geographical Information a primer

• Communicating with Cartography
• 29/10/2004

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TOPICS

• How does a map communicate?
• Thematic maps
• Topographic information
• Abstract maps
• Geographical Information Systems
• Practical info for NEXT WEEK

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How does a map communicate?

• Real word features are represented as points,
  lines, polygons, contours and symbols
• A map conveys a wide range of characteristics
  about the real world
• Size, length, distribution, patterns, contiguity,
  neighbourhood, space, shape and orientation

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Thematic maps

• Perhaps we should say - What do maps communicate?
• Thematic means theme based and a map can
  graphically communicate the spatial variability
  in a wide range of possible themes - both human
  (socio-economic) and physical

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Thematic Maps

• Population, death-rate, income levels etc are
  dynamic themes of data that will change rapidly
• Soils, geology, ecological zones and political
  maps will remain fairly static
• Themes may be presented as different colours or
  dots/shading - or even small pie-charts overlaid
  onto a normal political map

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Topographic maps

• Contours show areas of equal height above mean
  sea-level (MSL)
• Contours close together represent steep changes
  in height - contours far apart show gradual
  change in height
• Contours use an interval (in metres) although not
  all contours may be labelled

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Using contour maps

• Locate the nearest line to your feature
• If not labelled, locate nearest labelled line and
  multiply number of contours away by the interval
  then add (or subtract) this value from the
  nearest labelled contour value
• An alternative to using contours is a
  3-dimensional rendering of the surface

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Abstract Maps

• Maps do not always have to be accurate in terms
  of their representation of reality
• Maps can be abstract and may represent features
  of the real world in an ethereal way
• Maps can be used to suggest connections,
  principles or ideas that bear no parallel in
  reality. Such en entity is known as a cartogram

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Abstract maps

• Any kind of information can be communicated by a
  map
• Just as the London Underground was designed by an
  electronics draughtsman (Beck) in the 1920s, maps
  can be used to show power distribution - using
  clever abstraction and use of symbols

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Abstract maps

• Maps can also be used to provide a graphical
  representation of forecasts
• A map of a forecast variable (rainfall or
  temperature) is interesting as no such feature
  actually exists in reality.

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Abstract Maps

• Maps do not have to be 2 dimensional
• Detailed surveys of towns and cities have allowed
  computer generated 3-dimensional renderings to be
  generated

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GIS

• Geographical Information System (GIS)
• A GIS allows layers of spatially referenced
  information to be combined as though they were
  transparent slides
• A GIS can drill down through these layers to
  perform calculation, scenarios and model
  solutions to complex problems

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GIS

• A GIS must have a spatial reference framework.
  This can be latitude/longitude, Ordnance Survey
  grid, postcodes etc
• A GIS operates entirely within a computer system
• VECTOR features are represented as POINTS, LINES
  and POLYGONS

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GIS

• Some map data is continuous and is created from
  pixels. This type of data is known as RASTER data
• Raster data can be derived from satellite
  (rainfall, vegetation or a an aerial photograph)
• Raster data can be used in complex environmental
  models

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GIS

• Can be used for real-time applications
• Vector data stores metadata relating to any
  conceivable statistic in a separate database file
  that is spatially referenced within the map
• Raster data encodes continuous data as pixel
  values for a range of remotely sensed information

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Suggested Reading

• Mapping ways of representing the world by
  Dorling and Fairbairn, 1997
• ESRI map book. Implementing concepts of
  Geography. Volume 14, 1999
• Getting started with Geographical Information
  Systems by Clarke K., 1997

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PRACTICAL Today
Groups A2, B1 B2 (2pm 330pm) A1, C1 C2
(330pm 5pm) Loxford L106