1106: Geographical Information: a primer

Communicating with Cartography29/10/2004

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

GroupsA2, B1 & B2 (2pm – 3:30pm)

A1, C1 & C2 (3:30pm – 5pm)

Loxford: L106