1106: Geographical Information: a primer

Communicating with Cartography

29/10/2004

TOPICS

• How does a map communicate?

• Thematic maps

• Topographic information

• Abstract maps

• Geographical Information Systems

• Practical info for NEXT WEEK

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

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

Ocean

Life Expectancy39.8 - 49.549.5 - 5959 - 67.567.5 - 7373 - 79.3No Data

6000 0 6000 12000 Miles

N

EW

S

World

Ocean

Projected population in 20000.2 M - 16.4 M16.4 M - 48.5 M48.5 M - 107.5 M107.5 M - 270.1 M270.1 M - 1304.5 MNo Data

6000 0 6000 12000 Miles

N

EW

S

World

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

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

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

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

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

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.

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

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

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

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

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

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

PRACTICAL: Today

Groups

A2, B1 & B2 (2pm – 3:30pm)

A1, C1 & C2 (3:30pm – 5pm)

Loxford: L106